1000 (number)

"1,000"; "Thousand"; and "Chiliad" redirect here. For other uses, see 1000 (disambiguation) and Chiliarchy.

← 999 1000 1001 →
List of numbers Integers ← 0 1k 2k 3k 4k 5k 6k 7k 8k 9k →
Cardinal	one thousand
Ordinal	1000th (one thousandth)
Factorization	23 × 53
Divisors	1, 2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 125, 200, 250, 500, 1000
Greek numeral	,Α´
Roman numeral	M, m
Roman numeral (unicode)	M, m, ↀ
Unicode symbol	ↀ
Greek prefix	chilia
Latin prefix	milli
Binary	11111010002
Ternary	11010013
Senary	43446
Octal	17508
Duodecimal	6B412
Hexadecimal	3E816
Tamil	௲
Chinese	千
Punjabi	੧੦੦੦
Devanagari	१०००
Armenian	Ռ
Egyptian hieroglyph	𓆼

1000 or one thousand is the natural number following 999 and preceding 1001. In most English-speaking countries, it can be written with or without a comma or sometimes a period separating the thousands digit: 1,000.

A group of one thousand units is sometimes known, from Ancient Greek, as a chiliad. A period of one thousand years may be known as a chiliad or, more often from Latin, as a millennium. The number 1000 is also sometimes described as a short thousand in medieval contexts where it is necessary to distinguish the Germanic concept of 1200 as a long thousand. It is the first 4-digit integer.

Notation

• The decimal representation for one thousand is
  • 1000—a one followed by three zeros, in the general notation;
  • 1 × 10³—in engineering notation, which for this number coincides with:
  • 1 × 10³ exactly—in scientific normalized exponential notation;
  • 1 E+3 exactly—in scientific E notation.
• The SI prefix for a thousand units is "kilo-", abbreviated to "k"—for instance, a kilogram or "kg" is a thousand grams. This is sometimes extended to non-SI contexts, such as "ka" (kiloannum) being used as a shorthand for periods of 1000 years. In computer science, however, "kilo-" is used more loosely to mean 2 to the 10th power (1024 or 2¹⁰).
• In the SI writing style, a non-breaking space can be used as a thousands separator, i.e., to separate the digits of a number at every power of 1000.
• Multiples of thousands are occasionally represented by replacing their last three zeros with the letter "K" or "k": for instance, writing "$30k" for $30,000 or using "Y2K" to denote the Year 2000 computer problem.
• A thousand units of currency, especially dollars or pounds, are colloquially called a grand. In the United States, this is sometimes abbreviated with a "G" suffix.

In mathematics

A chiliagon is a 1000-sided polygon.

Numbers in the range 1001–1999

1001 to 1099

1001

Main article: 1001 (number)

1002

1002 = 2 × 3 × 167. It is a sphenic number, an abundant number, and a zero of Mertens function. There are 1002 partitions of 22.

1004

1004 = 2² × 251. It is a heptanacci number.

1006

1006 = 2 × 503. It is an unusual number, an equidigital number, and a square-free number. It is a record gap between twin primes. There are 1006 compositions (ordered partitions) of 22 into squares 1006 undirected Hamiltonian paths in 4 by 5 square grid graph.

1009

1009 is the smallest four-digit prime, a Lucky prime, and Chen prime. It is palindromic in bases 11, 15, 19, 24 and 28: (838₁₁, 474₁₅, 2F2₁₉, 1I1₂₄, 181₂₈).

1011

1011 = 3 × 337. It is a Harshad number in bases 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75 (and 202 other bases). It is the largest natural number n such that 2ⁿ contains 101 and does not contain 11011. There are 1011 partitions of 1 into reciprocals of positive integers <= 16 Egyptian fraction.

1012

1012 = 2² × 11 × 23. There are 1012 partitions of 1 into reciprocals of positive integers <= 17 Egyptian fraction.

1013

1013 is a prime number, a Sophie Germain prime, and a centered square number,

1016

1016 = 2³ × 127. It is stella octangula number and a member of the Mian–Chowla sequence. There are 1016 surface points on a cube with edge-length 14.

1019

1019 is a prime number, a Sophie Germain prime, a safe prime, and a Chen prime.

1021

1021 is a prime number, a Lucky prime, and a twin prime with 1019.

1023

Main article: 1023 (number)

1024

Main article: 1024 (number)

1025

1025 = 5² × 41. It is a Jacobsthal-Lucas number and the hypotenuse of a primitive Pythagorean triangle. It is a Proth number because 1025 = 2¹⁰ + 1. It is a member of the Moser–de Bruijn sequence because its base-4 representation (100001₄) contains only digits 0 and 1, or equivalently, it's a sum of distinct powers of 4 (4⁵ + 4⁰).

1028

1028 = 2² × 257. It is sum of totient function for first 58 integers. There are 1029 primes <= 2¹³.

1031

1031 is a prime number, a Sophie Germain prime, a super-prime, and a Chen prime. It is the exponent and number of ones for the fifth base-10 repunit prime.

1033

1033 is a prime number and an emirp. It forms a twin prime pair with 1031.

1035

1035 = 3² × 5 × 23. It is a hexagonal number and the 45th triangular number.

1039

1039 is a prime of the form 8n+7, a Chen prime, and a Lucky prime. There are 1039 partitions of 30 that do not contain 1 as a part.

1040

1040 = 2⁴ × 5 × 13. There are 1040 pieces that could be seen in a 6 × 6 × 6× 6 Rubik's Tesseract.

1046

1046 = 2 × 523. It is a coefficient of f(q), the 3rd order mock theta function.

1047

1047 = 3 × 349. There are 1047 ways to split a strict composition of 18 into contiguous subsequences that have the same sum.

1049

1049 is a prime number, a Sophie Germain prime, a highly cototient number, and a Chen prime.

1051

1051 is a prime number, a centered pentagonal number, and a centered decagonal number.

1056

1056 = 2⁵ × 3 × 11. It is a pronic number.

1059

1059 = 3 × 353. It is a number n such that n⁴ is written in the form of a sum of four positive 4th powers.

1060

1060 = 2² × 5 × 53. It is the sum of the first twenty-five primes from 2 through 97 (the number of primes less than 100) and the sixth sum of 10 consecutive primes, starting with 23 through 131.

1061

1061 is a prime number, an emirp, and a twin prime with 1063. There are 1061 prime numbers between 1000 and 10000 (or, number of four-digit primes in decimal representation).

1063

1063 is a prime number, a super-prime, a twin prime with 1061, a near-wall-sun-sun prime. and the sum of seven consecutive primes (137 + 139 + 149 + 151 + 157 + 163 + 167)

1069

1069 is a prime number and an emirp.

1076

1076 = 2² × 269. There are 1076 strict trees weight 11.

1078

1078 = 2 × 7² × 11. It is an Euler transform of negative integers.

1080

1080 = 2³ × 3³ × 5. It is a pentagonal number and a largely composite number.

1081

1081 = 23 × 47. It is the 46th triangular number and a member of Padovan sequence.

1086

1086 = 2 × 3 × 181. It is a Smith number and the sum of totient function for the first 59 integers.

1087

1087 is a prime number, a super-prime, a cousin prime, and a lucky prime.

1089

Main article: 1089 (number)

1091

1091 is a prime number, a cousin prime, and a twin prime with 1093.

1093

1093 is a twin prime with 1091. Together with 1091 and 1097, it forms a prime triplet. It is a happy prime and a star prime. It is also the smallest Wieferich prime. 1093 is a repunit prime in base 3 because:

$1093=1111111_{3}=3^{6}+3^{5}+3^{4}+3^{3}+3^{2}+3^{1}+3^{0}={\frac {3^{7}-1}{2}}\,.$

1096

1096 = 2³ × 137. There are 1096 strict solid partitions of 18.

1097

1097 is a prime number, an emirp, and a Chen prime.

1100 to 1199

1102

1102 = 2 × 19 × 29. It is the sum of the totient function for the first 60 integers.

1103

1103 is a prime number, a Sophie Germain prime, and a balanced prime.

1104

1104 = 2⁴ × 3 × 23. It is a Keith number

1105

Main article: 1105 (number)

1107

1107 = 3³ × 41. There are 1107 non-isomorphic strict T₀ multiset partitions of weight 8.

1109

1109 is a Friedlander-Iwaniec prime and a Chen prime.

1113

1113 = 3 × 7 × 53. There are 1113 strict partions of 40.

1114

1114 = 2 × 557. There are 1114 ways to write 22 as an orderless product of orderless sums.

1117

1117 is a Chen prime. There are 1117 diagonally symmetric polyominoes with 16 cells.

1118

1118 = 2 × 13 × 43. There are 1118 unimodular 2 × 2 matrices having all terms in {0,1,...,21}.

1119

1119 = 3 × 373. There are 1119 bipartite graphs with 9 nodes.

1122

1122 = 2 × 3 × 11 × 17. It is a pronic number.

1123

1123 is a balanced prime.

1124

1124 = 2² × 281. It is a Leyland number using 2 & 10: 1124 = 2¹⁰ + 10². It is a spy number.

1126

1126 = 2 × 563. There are 1126 2 × 2 non-singular integer matrices with entries from {0, 1, 2, 3, 4, 5}.

1127

1127 = 7² × 23. It is the maximum number of pieces that can be obtained by cutting an annulus with 46 cuts.

1128

1128 = 2³ × 3 × 47. It is the 47th triangular number and the 24th hexagonal number. 1128 is the dimensional representation of the largest vertex operator algebra with central charge of 24, D₂₄.

1129

1129 is a prime number. There are 1129 lattice points inside a circle of radius 19.

1130

1130 = 2 × 5 × 113. It is a skiponacci number.

1131

1131 = 3 × 13 × 29. There are 1131 edges in the hexagonal triangle T(26).

1132

1132 = 2² × 283. There are 1132 simple unlabeled graphs with 9 nodes of 2 colors whose components are complete graphs.

1133

1133 = 11 × 103. There are 1133 primitive subsequences of {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15}.

1135

1135 = 5 × 227. It is a centered triangular number.

1136

1136 = 2⁴ × 71. There are 1136 independent vertex sets and vertex covers in the 7-sunlet graph.

1137

1137 = 3 × 379. It is the sum of values of vertices at level 5 of the hyperbolic Pascal pyramid.

1139

1139 = 17 × 67. It is the wiener index of the windmill graph D(3,17).

1140

1140 = 2² × 3 × 5 × 19. It is a tetrahedral number.

1141

1141 = 7 × 163. It is a 7-Knödel number.

1142

1142 = 2 × 571. It is a spy number and a number n such that n³² + 1 is prime.

1143

1143 = 3² × 127. There are 1143 set partitions of 8 elements with 2 connectors.

1145

1145 = 5 × 229. It is a 5-Knödel number.

1150

1150 = 2 × 5² × 23. There are 1150 11-iamonds without bilateral symmetry.

1151

1151 is the first prime number following a prime gap of 22. It is also a Chen prime.

1152

1152 = 2⁷ × 3². It is a highly totient number, a 3-smooth number, and an Achilles number.

1153

1153 is a super-prime and a Proth prime.

1154

1154 = 2 × 577. Because 1154 = 2 × 24² + 2, there are 1154 points on the surface of tetrahedron with edge length 24.

1155

1155 = 3 × 5 × 7 × 11. It is the product of the first four odd primes. There are 1155 edges in the join of two cycle graphs of order 33.

1156

1156 = 2² × 17² = 34². It is an octahedral number, a centered pentagonal number, and a centered hendecagonal number.

1157

1157 = 13 × 89. It is the smallest number that can be written as n^2+1 without any prime factors of the form a^2+1.

1158

1158 = 2 × 3 × 193. There are 1158 points on surface of octahedron with edge length 17.

1159

1159 = 19 × 61. It is a centered octahedral number and a member of the Mian–Chowla sequence.

1160

1160 = 2³ × 5 × 29. It is an octagonal number.

1161

1161 = 3³ × 43. It is the sum of the first twenty-six primes.

1162

1162 = 2 × 7 × 83. It is the sum of the totient function for the first 61 integers and a pentagonal number.

1163

1163 is a Chen prime.

See also: Legendre's conjecture

1164

1164 = 2² × 3 × 97. There are 1164 chains of multisets that partition a normal multiset of weight 8, where a multiset is normal if it spans an initial interval of positive integers

1165

1165 = 5 × 233. It is a 5-Knödel number.

1169

1169 = 7 × 167. It is a highly cototient number

1171

1171 is a super-prime.

1173

1173 = 3 × 17 × 23. There are 1173 simple triangulations on a plane with 9 nodes.

1174

1174 = 2 × 587. There are 1174 widely totally strongly normal compositions of 16. (sequence A332337 in the OEIS).

1175

1175 = 5² × 47. It is the maximum number of pieces that can be obtained by cutting an annulus with 47 cuts.

1176

1176 = 2³ × 3 × 7². It is the 48th triangular number.

1178

1178 = 2 × 19 × 31. There are 1178 surface points on a cube with edge-length 15.

1179

1179 = 3² × 131. There are 1179 different permanents of binary 7 by 7 matrices.

1182

1182 = 2 × 3 × 197. There are 1182 necklaces possible with 14 beads of 2 colors (that cannot be turned over).

1184

1184 = 2⁵ × 37. It is an amicable number with 1210.

1186

1186 = 2 × 593. There are 1186 diagonally symmetric polyominoes with 15 cells.

1187

1187 is a safe prime, a Stern prime, a balanced prime, and a Chen prime.

1190

1190 = 2 × 5 × 7 × 17. It is a pronic number. Building a 28-tier house of cards requires 1190 cards.

1191

1191 = 3 × 397 = 35² - 35 + 1 = H₃₅, the 35th Hogben number.

1192

1192 = 2³ × 149. It is the sum of the totient function for the first 62 integers.

1193

1193 is a Chen prime.

4¹¹⁹³ - 3¹¹⁹³ is prime.

1194

1194 = 2 × 3 × 199. There are 1194 permutations that can be reached with 8 moves of 2 bishops and 1 rook on a 3 × 3 chessboard.

1196

1196 = 2² × 13 × 23 = $\sum _{k=1}^{38}\sigma (k)$.

1198

1198 = 2 × 599. It is a centered heptagonal number.

1199

1199 = 11 × 109. It is the area of the 20th conjoined trapezoid.

1200 to 1299

1200

1200 = 2⁴ × 3 × 5². There are 1200 households in the Nielsen ratings sample.

1200 is known as the long thousand or ten "long hundreds" of 120 each. It is the traditional reckoning of large numbers in Germanic languages.

1201

1201 is a super-prime, a centered square number, and a centered decagonal number.

1202

1202 = 2 × 601. There are a maximum of 1202 regions when the plane is divided by 25 ellipses.

1203

1203 = 3 × 401. It is the smallest number greater than 1000 in the coordinating sequence for the (2,6,∞) tiling of the hyperbolic plane.

1204

1204 = 2² × 7 × 43. It is the magic constant for a 7 × 7 × 7 magic cube.

1205

1205 = 5 × 241. There are 1205 partitions of 28 such that the number of odd parts is a part

1207

1207 = 17 × 71. It is a composite de Polignac number.

1208

1208 = 2³ × 151. There are 1208 strict chains of divisors starting with the superprimorial A006939(3).

1210

1210 = 2 × 5 × 11². It is an amicable number with 1184 and a Self-descriptive number.

1211

1211 = 7 × 173. It is a composite de Polignac number

1212

1212 = 2² × 3 × 101 = $\sum _{k=0}^{17}p(k)$, where $p(k)$ is the number of partions of $k$.

1213

1213 is a prime number and an emirp.

1214

1214 = 2 × 607. It is a spy number and the sum of the first 39 composite numbers.

1215

1215 = 3⁵ × 5. There are 1215 edges in the hexagonal triangle T(27)

1216

1216 = 2⁶ × 19. It is a nonagonal number

1217

1217 is a super-prime and a Proth prime.

1219

1219 = 23 × 53. It is a centered triangular number and a zero of Mertens function.

1220

1220 = 2² × 5 × 61. It is a zero of Mertens function. There are 1220 binary vectors of length 16 containing no singletons.

1222

1222 = 2 × 13 × 47. It is a hexagonal pyramidal number.

1223

1223 is the 200th prime number. It is also a Sophie Germain prime and a balanced prime.

1224

1224 = 2³ × 3² × 17. There are 1224 edges in the join of two cycle graphs, both of order 34.

1225

1225 = 5² × 7² = 35². It is the smallest number greater than 1 to be a triangular number, a square number and a hexagonal number. It is the second square triangular number greater than 1. It is the 49th triangular number, the 35th square number, the 25th hexagonal number, a centered octagonal number, a 29-gonal number, a 60-gonal number, and a 124-gonal number. It is the sum of 5 consecutive odd cubes:

1225 = 1³ + 3³ + 5³ + 7³ + 9³.

1226

1226 = 2 × 613. There are 1226 rooted identity trees with 15 nodes.

1228

1228 = 2² × 307. It is the sum of the totient function for the first 63 integers.

1229

1229 is a Sophie Germain prime and an emirp. There are 1229 primes less than 10,000.

1230

1230 = 2 × 3 × 5 × 41 = T(9, 6), the Mahonian number.

1231

1231 is a prime number and an emirp.

1232

1232 = 2⁴ × 7 × 11. There are 1232 labeled ordered set of partitions of a 7-set into odd parts.

1234

1234 = 2 × 617. It has two distinct prime factors making it a squarefree semiprime. It is the smallest whole number containing all numbers from 1 to 4. There are 1234 parts in all partitions of 30 into distinct parts. There are 1234 independent vertex sets in a 4×4 square grid. Equivalently, there are 1234 distinct 4×4 binary matrices in which no two adjacent elements are both equal to 1.

A 2012 study of frequently-used personal identification numbers (PIN) found that, among 4-digit PIN codes, 1234 is the most frequently chosen.

1236

1236 = 2² × 3 × 103 = 617 + 619, the sum of a twin prime pair.

1238

1238 = 2 × 619. There are 1238 partitions of 31 that do not contain 1 as a part.

1239

1239 = 3 × 7 × 59. It is a toothpick number in 3 dimensions.

1240

1240 = 2³ × 5 × 31. It is a square pyramidal number.

1241

1241 = 17 × 73. It is a centered cube number and a spy number.

1243

1243 = 11 × 113. It is a composite de Polignac number.

1244

1244 = 2² × 311. There are 1244 complete partitions of 25.

1245

1245 = 3 × 5 × 83. There are 1245 labeled spanning intersecting set-systems on 5 vertices.

1247

1247 = 29 × 43. It is a pentagonal number.

1249

1249 is a prime number, an emirp, and a trimorphic number.

1251

1251 = 3² × 139. Because 1251 = 2 × 25² + 1, there are 1251 different determinants of 2 × 2 matrices with integer entries from 0 to 25.

1252

1252 = 2² × 313. Because 1252 = 2 × 25² + 2, there are 1252 points on the surface of a tetrahedron with edgelength 25.

1255

1255 = 5 × 251. It is a zero of Mertens function. There are 1255 of partitions of 23. There are 1255 ways to write 23 as an orderless product of orderless sums.

1257

1257 = 3 × 419. There are 1257 lattice points inside a circle of radius 20.

1259

1259 is a prime number and a highly cototient number.

1260

1260 = 2² × 3² × 5 × 7. It is a pronic number, the smallest vampire number, the 16th highly composite number, and the sum of the totient function for the first 64 integers. There are 1260 strict partions of 41.

1261

1261 = 13 × 97. It is a star number and a zero of Mertens function.

1264

1264 = 2⁴ × 79. It is the sum of the first 27 primes.

1265

1265 = 5 × 11 × 23. There are 1265 rooted trees with 43 vertices in which vertices at the same level have the same degree.

1266

1266 = 2 × 3 × 211. It is a centered pentagonal number and a zero of Mertens function.

1267

1267 = 7 × 181. It is a 7-Knödel number.

1269

1269 = 3³ × 47. Completing 11 revolutions in the Spiral of Theodorus requires 1269 triangles.

1275

1275 = 3 × 5² × 17. It is the 50th triangular number.

1276

1276 = 2² × 11 × 29. There are 1276 irredundant sets in the 25-cocktail party graph.

1277

1277 is a prime number. It is the start of a prime constellation of length 9 (a "prime nonuple").

1278

1278 = 2 × 3² × 71. There are 1278 Narayana's cows and calves after 20 years.

1279

1279 is a prime number and a Mersenne prime exponent.

1280

1280 = 2⁸ × 5. There are 1280 parts in all compositions of 9.

1281

1281 = 3 × 7 × 61. It is an octagonal number.

1283

1283 is a safe prime.

1284

1284 = 2² × 3 × 107 = 641 + 643, the sum of a twin prime pair.

1285

1285 = 5 × 257. There are 1285 free nonominoes.

1286

1286 = 2 × 643. There are 1286 inequivalent connected planar figures that can be formed from five 1 X 2 rectangles (or dominoes) such that each pair of touching rectangles shares exactly one edge, of length 1, and the adjacency graph of the rectangles is a tree.

1287

1287 = 3² × 11 × 13 = ${13 \choose 5}$.

1288

1288 = 2³ × 7 × 23. It is a heptagonal number.

1289

1289 is Sophie Germain prime and a twin prime with 1291. 1289 is a deficient number because the sum of all its positive divisors (except itself) totals less than 1289. 1289 is an evil number because it has an even number of 1's contained in its binary expansion.

1291

1291 is a twin prime with 1289.

1292

1292 = 2² × 17 × 19. phi(1292) = phi(sigma(1292)).

1295

1295 = 5 × 7 × 37. There are 1295 edges in the join of two cycle graphs, both of order 35.

1296

1296 = 2⁴ × 3⁴ = 6⁴ = 36². It is the sum of the cubes of the first eight positive integers:

1³ + 2³ + 3³ + 3³ + 4³ + 5³ + 6³ + 7³ + 8³ = 1296.

There are 1296 rectangles on a normal 8 × 8 chessboard. There are 1296 combinations of 2 alphanumeric characters.

1297

1297 is a super-prime, a pinwheel number, and a zero of Mertens function.

1300 to 1399

1300

1300 = 2² × 5² × 13. It is a zero of Mertens function and the smallest even odd-factor hyperperfect number. It is the sum of the first 4 fifth powers:

1300 = 1⁵ + 2⁵ + 3⁵ + 4⁵.

1301

1301 is a prime number and a centered square number. There are 1301 trees with 13 unlabeled nodes.

1306

1306 = 2 × 653. It is a centered triangular number.

1307

1307 is a safe prime.

1308

1308 = 2² × 3 × 109. It is the sum of the totient function for the first 65 integers.

1312

1312 = 2⁵ × 41. It is a member of the Mian-Chowla sequence.

1316

1316 = 2² × 7 × 47. It is the Euler transformation of sigma(11).

1319

1319 is a safe prime.

1320

1320 = 2³ × 3 × 5 × 11 = 659 + 661, the sum of a twin prime pair.

1325

1325 = 5² × 53. It is a Markov number and a centered tetrahedral number.

1326

1326 = 2 × 3 × 13 × 17. It is the 51st triangular number and a hexagonal number.

1327

1327 is the smallest prime number preceding a prime gap of 34.

1328

1328 = 2⁴ × 83. It is the sum of the totient function for the first 66 integers.

1330

1330 = 2 × 5 × 7 × 19. It is a tetrahedral number. It forms a Ruth–Aaron pair with 1331 under second definition.

1331

1331 = 11³. It is a centered heptagonal number. It forms a Ruth–Aaron pair with 1330 under second definition.

1334

1334 = 2 × 23 × 29. The maximal number of regions the plane can be divided into by drawing 37 circles is 1334.

1335

1335 = 3 × 5 × 89. It is a pentagonal number.

1342

1342 = 2 × 11 × 61 = $\sum _{k=1}^{40}\sigma (k)$.

1346

1346 = 2 × 673. There are 1346 locally disjointed rooted trees with 10 nodes.

1350

1350 = 2 × 3³ × 5². It is a nonagonal number.

1353

1353 = 3 × 11 × 41. Because 1353 = 2 × 26² + 1, there are 1353 different 2 × 2 determinants with integer entries from 0 to 26.

1361

1361 is first prime number following a prime gap of 34 and the 3rd Mills' prime. It is a centered decagonal number.

1363

1363 = 29 × 47. There are 1363 ways to modify a circular arrangement of 14 objects by swapping one or more adjacent pairs.

1364

1364 = 2² × 11 × 31. It is a Lucas number.

1365

1365 = 3 × 5 × 7 × 13. It is a pentatope number.

1367

1367 is a safe prime and a balanced prime. It is the sum of three, nine, and eleven consecutive primes: (449 + 457 + 461, 131 + 137 + 139 + 149 + 151 + 157 + 163 + 167 + 173, and 101 + 103 + 107 + 109 + 113 + 127 + 131 + 137 + 139 + 149 + 151),

1368

1368 = 2³ × 3² × 19. There are 1368 edges in the join of two cycle graphs, both of order 36.

1371

1371 = 3 × 457. It is the sum of the first 28 primes.

1373

1373 is a prime number. There are 1373 lattice points inside a circle of radius 21

1377

1377 = 3⁴ × 17. It is the maximal number of pieces that can be obtained by cutting an annulus with 51 cuts

1378

1378 = 2 × 13 × 53. It is the 52nd triangular number

1379

1379 = 7 × 197. It is the magic constant of n × n normal magic square and n-queens problem for n = 14.

1380

1380 = 2² × 3 × 5 × 23. There are 1380 8-step mappings with 4 inputs.

1381

1381 is a prime number and a centered pentagonal number.

1384

1384 = 2³ × 173 = $\sum _{k=1}^{41}\sigma (k)$

1385

1385 = 5 × 277. It is an up/down number.

1387

1387 = 19 × 73. It is the 5th Fermat pseudoprime of base 2, the 22nd centered hexagonal number, the 19th decagonal number, and the second Super-Poulet number.

1388

1388 = 2² × 347. Because 1388 = 4 × 19² - 3 × 19 + 1, is on the x-axis of Ulams spiral.

1393

1393 = 7 × 199. It is a 7-Knödel number.

1394

1394 = 2 × 17 × 41. It is the sum of the totient function for the first 67 integers.

1395

1395 = 3² × 5 × 19. It is a vampire number and a member of the Mian–Chowla sequence

1369

1396 = 2² × 349. It is a centered triangular number.

1399

1399 is a prime number and an emirp.

1400 to 1499

1403

1403 = 23 × 61. It is the smallest number x such that M(x) = 11, where M() is Mertens function

1404

1404 = 2² × 3² × 13. It is a heptagonal number.

1405

1405 = 5 × 281 = 26² + 27² = 7² + 8² + ... + 16². It is a centered square number

1406

1406 = 2 × 19 × 37. It is a semi-meandric number.

1409

1409 is a super-prime, a Sophie Germain prime, and a Proth prime.

1410

1410 = 2 × 3 × 5 × 47. It is the denominator of the 46th Bernoulli number

1418

1418 = 2 × 709. It is the smallest number x such that M(x) = 13, where M() is Mertens function

1425

1425 = 3 × 5² × 19. It is a self-descriptive number in base 5.

1426

1426 = sum of totient function for first 68 integers, pentagonal number, number of strict partions of 42

1427

1427 = twin prime together with 1429

1428

1428 = number of complete ternary trees with 6 internal nodes, or 18 edges;

1429

1429 = twin prime together with 1427

1430

1430 = Catalan number

1431

1431 = 53rd triangular number, hexagonal number

1432

1432 = member of Padovan sequence

1433

1433 = super-prime,

1435

1435 = vampire number;

1436

1436 = discriminant of a totally real cubic field

1437

1437 = smallest number of complexity 20: smallest number requiring 20 1's to build using +, * and ^

1439

1439 = Sophie Germain prime, safe prime

1440

1440 = a highly totient number, a largely composite number

1441

1441 = star number

1447

1447 = super-prime, happy number

1451

1451 = Sophie Germain prime

1452

1452 = first Zagreb index of the complete graph K₁₂

1453

1453 = Sexy prime with 1459

1458

1458 = 2 × 3⁶. It is the maximum determinant of an 11 by 11 matrix of zeroes and ones and a 3-smooth number.

1458 is one of three numbers which, when its base 10 digits are added together, produces a sum which, when multiplied by its reversed self, yields the original number:

1 + 4 + 5 + 8 = 18

18 × 81 = 1458

The only other non-trivial numbers with this property are 81 and 1729, as well as the trivial solutions 1 and 0. It was proven by Masahiko Fujiwara.

1459

1459 = Sexy prime with 1453, sum of nine consecutive primes (139 + 149 + 151 + 157 + 163 + 167 + 173 + 179 + 181), Pierpont prime

1462

1462 = (35 - 1) × (35 + 8) = the first Zagreb index of the wheel graph with 35 vertices

1465

1465 = 5-Knödel number

1466

1466 = $\sum _{k=1}^{256}d(k)$, where $d(k)$ = number of divisors of $k$

1467

1467 = number of partitions of 39 with zero crank

• 1469 = octahedral number, highly cototient number
• 1470 = pentagonal pyramidal number, sum of totient function for first 69 integers
• 1471 = super-prime, centered heptagonal number
• 1476 = coreful perfect number
• 1477 = 7-Knödel number
• 1480 = sum of the first 29 primes
• 1481 = Sophie Germain prime
• 1485 = 54th triangular number
• 1486 = number of strict solid partitions of 19
• 1487 = safe prime
• 1489 = centered triangular number
• 1490 = tetranacci number
• 1491 = nonagonal number,
• 1492 = discriminant of a totally real cubic field,
• 1493 = Stern prime
• 1494 = sum of totient function for first 70 integers
• 1496 = square pyramidal number
• 1499 = Sophie Germain prime, super-prime

1500 to 1599

• 1500 = hypotenuse in three different Pythagorean triangles
• 1501 = centered pentagonal number
• 1502 = number of pairs of consecutive integers x, x+1 such that all prime factors of both x and x+1 are at most 47
• 1503 = least number of triangles of the Spiral of Theodorus to complete 12 revolutions
• 1504 = primitive abundant number (abundant number all of whose proper divisors are deficient numbers)
• 1508 = heptagonal pyramidal number
• 1509 = pinwheel number
• 1510 = deficient number, odious number
• 1511 = Sophie Germain prime, balanced prime
• 1513 = centered square number
• 1516 = $\left\lfloor 9^{\frac {10}{3}}\right\rfloor$
• 1517 = number of lattice points inside a circle of radius 22
• 1519 = number of polyhexes with 8 cells, Mertens function zero
• 1520 = pentagonal number, Mertens function zero, forms a Ruth–Aaron pair with 1521 under second definition
• 1521 = 39², Mertens function zero, centered octagonal number, forms a Ruth–Aaron pair with 1520 under second definition
• 1523 = super-prime, Mertens function zero, safe prime, member of the Mian–Chowla sequence
• 1525 = heptagonal number,
• 1526 = number of conjugacy classes in the alternating group A₂₇
• 1527 = number of 2-dimensional partitions of 11,
• 1529 = composite de Polignac number
• 1530 = vampire number
• 1531 = prime number, centered decagonal number, Mertens function zero
• 1532 = number of series-parallel networks with 9 unlabeled edges, Mertens function zero
• 1535 = Thabit number
• 1536 = a common size of microplate, 3-smooth number (2⁹×3), number of threshold functions of exactly 4 variables
• 1537 = Keith number,
• 1539 = maximal number of pieces that can be obtained by cutting an annulus with 54 cuts
• 1540 = 55th triangular number, hexagonal number, decagonal number, tetrahedral number
• 1541 = octagonal number
• 1543 = prime dividing all Fibonacci sequences,
• 1546 = number of 5 X 5 binary matrices with at most one 1 in each row and column, Mertens function zero
• 1547 = hexagonal pyramidal number
• 1548 = coreful perfect number
• 1549 = de Polignac prime
• 1550 = ${\frac {31\times (3\times 31+7)}{2}}$ = number of cards needed to build a 31-tier house of cards with a flat, one-card-wide roof
• 1552 = Number of partitions of 57 into prime parts
• 1556 = sum of the squares of the first nine primes
• 1557 = number of graphs with 8 nodes and 13 edges
• 1559 = Sophie Germain prime
• 1561 = a centered octahedral number, number of series-reduced trees with 19 nodes
• 1562 = maximal number of regions the plane is divided into by drawing 40 circles
• 1563 = $\sum _{k=1}^{50}{\frac {50}{\gcd(50,k)}}$
• 1564 = sum of totient function for first 71 integers
• 1565 = ${\sqrt {1036^{2}+1173^{2}}}$ and $1036+1173=47^{2}$
• 1566 = number k such that k⁶⁴ + 1 is prime
• 1567 = number of partitions of 24 with at least one distinct part
• 1568 = Achilles number
• 1569 = 2 × 28² + 1 = number of different 2 × 2 determinants with integer entries from 0 to 28
• 1570 = 2 × 28² + 2 = number of points on surface of tetrahedron with edgelength 28
• 1571 = Honaker prime
• 1572 = member of the Mian–Chowla sequence
• 1573 = discriminant of a totally real cubic field
• 1575 = odd abundant number, sum of the nontriangular numbers between successive triangular numbers, number of partitions of 24
• 1583 = Sophie Germain prime
• 1585 = Riordan number, centered triangular number
• 1587 = 3 × 23² = number of edges of a complete tripartite graph of order 69, K_23,23,23
• 1588 = sum of totient function for first 72 integers
• 1589 = composite de Polignac number
• 1592 = sum of all divisors of the first 36 odd numbers
• 1593 = sum of the first 30 primes
• 1594 = minimal cost of maximum height Huffman tree of size 17
• 1595 = number of non-isomorphic set-systems of weight 10
• 1596 = 56th triangular number
• 1597 = Fibonacci prime, Markov prime, super-prime, emirp
• 1599 = number of edges in the join of two cycle graphs, both of order 39

1600 to 1699

• 1600 = 40², repdigit in base 7 (4444₇),
• 1601 = Sophie Germain prime, Proth prime,
• 1602 = number of points on surface of octahedron with edgelength 20
• 1603 = number of partitions of 27 with nonnegative rank
• 1604 = number of compositions of 22 into prime parts
• 1605 = number of polyominoes consisting of 7 regular octagons
• 1607 = member of prime triple with 1609 and 1613
• 1608 = $\sum _{k=1}^{44}\sigma (k)$
• 1610 = number of strict partions of 43
• 1611 = number of rational numbers which can be constructed from the set of integers between 1 and 51
• 1612 = maximum dimension of Euclidean spaces which suffice for every smooth compact Riemannian 31-manifold to be realizable as a sub-manifold
• 1613, 1607 and 1619 are all primes
• 1614 = number of ways of refining the partition 8^1 to get 1^8
• 1615 = composite number such that the square mean of its prime factors is a nonprime integer
• 1616 = ${\frac {16(16^{2}+3\times 16-1)}{3}}$ = number of monotonic triples (x,y,z) in {1,2,...,16}³
• 1617 = pentagonal number
• 1618 = centered heptagonal number
• 1619 = palindromic prime in binary, safe prime
• 1620 = 809 + 811: sum of twin prime pair
• 1621 = super-prime, pinwheel number
• 1622 = semiprime of the form prime + 1
• 1623 is not the sum of two triangular numbers and a fourth power
• 1624 = number of squares in the Aztec diamond of order 28
• 1625 = centered square number
• 1626 = centered pentagonal number
• 1628 = centered pentagonal number
• 1629 = rounded volume of a regular tetrahedron with edge length 24
• 1631 = $\sum _{k=0}^{5}(k+1)!{\binom {5}{k}}$
• 1632 = number of acute triangles made from the vertices of a regular 18-polygon
• 1633 = star number
• 1634 = the smallest four-digit Narcissistic number in base 10
• 1635 = number of partitions of 56 whose reciprocal sum is an integer
• 1637 = prime island: least prime whose adjacent primes are exactly 30 apart
• 1638 = harmonic divisor number, 5 × 2¹⁶³⁸ - 1 is prime
• 1639 = nonagonal number
• 1640 = pronic number
• 1641 = 41² - 41 + 1 = H₄₁ (the 41st Hogben number)
• 1642 = maximal number of regions the plane is divided into by drawing 41 circles
• 1643 = sum of first 46 composite numbers
• 1644 = 821 + 823: sum of twin prime pair
• 1645 = number of 16-celled pseudo still lifes in Conway's Game of Life, up to rotation and reflection
• 1646 = number of graphs with 8 nodes and 14 edges
• 1647 and 1648 are both divisible by cubes
• 1648 = number of partitions of 34³ into distinct cubes
• 1649 = highly cototient number, Leyland number using 4 & 5 (4⁵ + 5⁴)
• 1650 = number of cards to build an 33-tier house of cards
• 1651 = heptagonal number
• 1652 = number of partitions of 29 into a prime number of parts
• 1653 = 57th triangular number, hexagonal number, number of lattice points inside a circle of radius 23
• 1654 = number of partitions of 42 into divisors of 42
• 1656 = 827 + 829: sum of twin prime pair
• 1657 = cuban prime,
• 1658 = smallest composite that when added to sum of prime factors reaches a prime after 25 iterations
• 1659 = number of rational numbers which can be constructed from the set of integers between 1 and 52
• 1660 = sum of totient function for first 73 integers
• 1661 = 11 × 151, palindrome that is a product of two palindromic primes
• 1662 = number of partitions of 49 into pairwise relatively prime parts
• 1663 = a prime number and 5¹⁶⁶³ - 4¹⁶⁶³ is a 1163-digit prime number
• 1664 = k such that k, k+1 and k+2 are sums of 2 squares
• 1665 = centered tetrahedral number
• 1666 = largest efficient pandigital number in Roman numerals (each symbol occurs exactly once)
• 1667 = 228 + 1439 and the 228th prime is 1439
• 1668 = number of partitions of 33 into parts all relatively prime to 33
• 1669 = super-prime, smallest prime with a gap of exactly 24 to the next prime
• 1670 = number of compositions of 12 such that at least two adjacent parts are equal
• 1671 divides the sum of the first 1671 composite numbers
• 1672 = 41² - 3², the only way to express 1672 as a difference of prime squares
• 1676 = number of partitions of 34 into parts each of which is used a different number of times
• 1679 = highly cototient number, semiprime (23 × 73, see also Arecibo message), number of parts in all partitions of 32 into distinct parts
• 1680 = the 17th highly composite number, number of edges in the join of two cycle graphs, both of order 40
• 1681 = 41², smallest number yielded by the formula n² + n + 41 that is not a prime; centered octagonal number
• 1682 and 1683 is a member of a Ruth–Aaron pair (first definition)
• 1683 = triangular matchstick number
• 1684 = centered triangular number
• 1685 = 5-Knödel number
• 1686 = $\sum _{k=1}^{45}\sigma (k)$
• 1687 = 7-Knödel number
• 1688 = number of finite connected sets of positive integers greater than one with least common multiple 72
• 1689 = $9!!\sum _{k=0}^{4}{\frac {1}{2k+1}}$
• 1690 = number of compositions of 14 into powers of 2
• 1691 = the same upside down, which makes it a strobogrammatic number
• 1692 = coreful perfect number
• 1695 = magic constant of n × n normal magic square and n-queens problem for n = 15. Number of partitions of 58 into prime parts
• 1696 = sum of totient function for first 74 integers
• 1698 = number of rooted trees with 47 vertices in which vertices at the same level have the same degree
• 1699 = number of rooted trees with 48 vertices in which vertices at the same level have the same degree

1700 to 1799

• 1700 = σ₂(39): sum of squares of divisors of 39
• 1702 = palindromic in 3 consecutive bases: 898₁₄, 787₁₅, 6A6₁₆
• 1705 = tribonacci number
• 1706 = 1 + 4 + 16 + 64 + 256 + 1024 + 256 + 64 + 16 + 4 + 1 sum of fifth row of triangle of powers of 4
• 1710 = maximal number of pieces that can be obtained by cutting an annulus with 57 cuts
• 1711 = 58th triangular number, centered decagonal number
• 1712 = number of irredundant sets in the 29-cocktail party graph
• 1713 = number of aperiodic rooted trees with 12 nodes
• 1716 = 857 + 859: sum of twin prime pair,
• 1717 = pentagonal number
• 1718 = $\sum _{d|12}{\binom {12}{d}}$
• 1719 = composite de Polignac number
• 1720 = sum of the first 31 primes
• 1721 = twin prime; number of squares between 42² and 42⁴.
• 1722 = Giuga number, pronic number
• 1723 = super-prime
• 1724 = maximal number of regions the plane is divided into by drawing 42 circles
• 1725 = 47² - 22² = (prime(15))² - (nonprime(15))²
• 1726 = number of partitions of 44 into distinct and relatively prime parts
• 1727 = area of the 24th conjoined trapezoid
• 1728 = the quantity expressed as 1000 in duodecimal, that is, the cube of twelve (called a great gross), and so, the number of cubic inches in a cubic foot, palindromic in base 11 (1331₁₁) and 23 (363₂₃)
• 1729 = taxicab number, Carmichael number, Zeisel number, centered cube number, Hardy–Ramanujan number. In the decimal expansion of e the first time all 10 digits appear in sequence starts at the 1729th digit (or 1728th decimal place). In 1979 the rock musical Hair closed on Broadway in New York City after 1729 performances. Palindromic in bases 12, 32, 36.
• 1730 = 3 × 24² + 2 = number of points on surface of square pyramid of side-length 24
• 1732 = $\sum _{k=0}^{5}{\binom {5}{k}}^{k}$
• 1733 = Sophie Germain prime, palindromic in bases 3, 18, 19.
• 1736 = sum of totient function for first 75 integers, number of surface points on a cube with edge-length 18
• 1737 = pinwheel number
• 1740 = number of squares in the Aztec diamond of order 29
• 1741 = super-prime, centered square number
• 1742 = number of regions the plane is divided into by 30 ellipses
• 1743 = wiener index of the windmill graph D(3,21)
• 1745 = 5-Knödel number
• 1746 = number of unit-distance graphs on 8 nodes
• 1747 = balanced prime
• 1748 = number of partitions of 55 into distinct parts in which the number of parts divides 55
• 1749 = number of integer partitions of 33 with no part dividing all the others
• 1750 = hypotenuse in three different Pythagorean triangles
• 1751 = cropped hexagone
• 1753 = balanced prime
• 1755 = number of integer partitions of 50 whose augmented differences are distinct
• 1756 = centered pentagonal number
• 1757 = least number of triangles of the Spiral of Theodorus to complete 13 revolutions
• 1758 = $\sum _{k=1}^{46}\sigma (k)$
• 1759 = de Polignac prime
• 1762 = number of binary sequences of length 12 and curling number 2
• 1763 = number of edges in the join of two cycle graphs, both of order 41
• 1765 = number of stacks, or planar partitions of 15
• 1769 = maximal number of pieces that can be obtained by cutting an annulus with 58 cuts
• 1770 = 59th triangular number, hexagonal number, Seventeen Seventy, town in Australia
• 1771 = tetrahedral number
• 1772 = centered heptagonal number, sum of totient function for first 76 integers
• 1774 = number of rooted identity trees with 15 nodes and 5 leaves
• 1776 = 24th square star number. The number of pieces that could be seen in a 7 × 7 × 7× 7 Rubik's Tesseract.
• 1780 = number of lattice paths from (0, 0) to (7, 7) using E (1, 0) and N (0, 1) as steps that horizontally cross the diagonal y = x with even many times
• 1781 = the first 1781 digits of e form a prime
• 1782 = heptagonal number
• 1783 = de Polignac prime
• 1784 = number of subsets of {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12} such that every pair of distinct elements has a different quotient
• 1785 = square pyramidal number, triangular matchstick number
• 1786 = centered triangular number
• 1787 = super-prime, sum of eleven consecutive primes (137 + 139 + 149 + 151 + 157 + 163 + 167 + 173 + 179 + 181 + 191)
• 1788 = Euler transform of -1, -2, ..., -34
• 1790 = number of partitions of 50 into pairwise relatively prime parts
• 1791 = largest natural number that cannot be expressed as a sum of at most four hexagonal numbers.
• 1792 = Granville number
• 1793 = number of lattice points inside a circle of radius 24
• 1794 = nonagonal number, number of partitions of 33 that do not contain 1 as a part
• 1795 = number of heptagons with perimeter 38
• 1799 = 2 × 30² − 1 = a twin square

1800 to 1899

• 1801 = cuban prime, sum of five and nine consecutive primes (349 + 353 + 359 + 367 + 373 and 179 + 181 + 191 + 193 + 197 + 199 + 211 + 223 + 227)
• 1803 = number of decahexes that tile the plane isohedrally but not by translation or by 180-degree rotation (Conway criterion)
• 1806 = pronic number, product of first four terms of Sylvester's sequence, primary pseudoperfect number, only number for which n equals the denominator of the nth Bernoulli number, Schröder number
• 1807 = fifth term of Sylvester's sequence
• 1808 = maximal number of regions the plane is divided into by drawing 43 circles
• 1809 = sum of first 17 super-primes
• 1810 = $\sum _{k=0}^{4}{\binom {4}{k}}^{4}$
• 1811 = Sophie Germain prime
• 1813 = number of polyominoes with 26 cells, symmetric about two orthogonal axes
• 1814 = 1 + 6 + 36 + 216 + 1296 + 216 + 36 + 6 + 1 = sum of 4th row of triangle of powers of six
• 1817 = total number of prime parts in all partitions of 20
• 1820 = pentagonal number, pentatope number, number of compositions of 13 whose run-lengths are either weakly increasing or weakly decreasing
• 1821 = member of the Mian–Chowla sequence
• 1822 = number of integer partitions of 43 whose distinct parts are connected
• 1823 = super-prime, safe prime
• 1824 = 43² - 5², the only way to express 1824 as a difference of prime squares
• 1825 = octagonal number
• 1826 = decagonal pyramidal number
• 1827 = vampire number
• 1828 = meandric number, open meandric number, appears twice in the first 10 decimal digits of e
• 1829 = composite de Polignac number
• 1830 = 60th triangular number
• 1831 = smallest prime with a gap of exactly 16 to next prime (1847)
• 1832 = sum of totient function for first 77 integers
• 1833 = number of atoms in a decahedron with 13 shells
• 1834 = octahedral number, sum of the cubes of the first five primes
• 1835 = absolute value of numerator of $D_{6}^{(5)}$
• 1836 = factor by which a proton is more massive than an electron
• 1837 = star number
• 1841 = solution to the postage stamp problem with 3 denominations and 29 stamps,
• 1842 = number of unlabeled rooted trees with 11 nodes
• 1843 = k such that phi(k) is a perfect cube, Mertens function zero
• 1844 = 3⁷ - 7³, Mertens function zero
• 1845 = number of partitions of 25 containing at least one prime, Mertens function zero
• 1847 = super-prime
• 1848 = number of edges in the join of two cycle graphs, both of order 42
• 1849 = 43², palindromic in base 6 (= 12321₆), centered octagonal number
• 1850 = Number of partitions of 59 into prime parts
• 1851 = sum of the first 32 primes
• 1853 = sum of primitive roots of 27-th prime, Mertens function zero
• 1854 = number of permutations of 7 elements with no fixed points, Mertens function zero
• 1855 = rencontres number: number of permutations of [7] with exactly one fixed point
• 1856 = sum of totient function for first 78 integers
• 1857 = Mertens function zero, pinwheel number
• 1858 = number of 14-carbon alkanes C₁₄H₃₀ ignoring stereoisomers
• 1859 = composite de Polignac number
• 1860 = number of squares in the Aztec diamond of order 30
• 1861 = centered square number, Mertens function zero
• 1862 = forms a Ruth–Aaron pair with 1863 under second definition
• 1863 = forms a Ruth–Aaron pair with 1862 under second definition
• 1865 = 12345₆: Largest senary metadrome (number with digits in strict ascending order in base 6)
• 1866 = number of plane partitions of 16 with at most two rows
• 1867 = prime de Polignac number
• 1868 = smallest number of complexity 21: smallest number requiring 21 1's to build using +, * and ^
• 1870 = decagonal number
• 1871 = the first prime of the 2 consecutive twin prime pairs: (1871, 1873) and (1877, 1879)
• 1872 = first Zagreb index of the complete graph K₁₃
• 1873 = number of Narayana's cows and calves after 21 years
• 1880 = the 10th element of the self convolution of Lucas numbers
• 1881 = tricapped prism number
• 1882 = number of linearly separable Boolean functions in 4 variables
• 1883 = number of conjugacy classes in the alternating group A₂₈
• 1886 = number of partitions of 6⁴ into fourth powers
• 1887 = number of edges in the hexagonal triangle T(34)
• 1889 = Sophie Germain prime, highly cototient number
• 1891 = 61st triangular number, sum of 5 consecutive primes (367 + 373 + 379 + 383 + 389) hexagonal number, centered pentagonal number, centered triangular number
• 1892 = pronic number
• 1894 = maximal number of regions the plane is divided into by drawing 44 circles
• 1896 = member of the Mian-Chowla sequence
• 1897 = member of Padovan sequence, number of triangle-free graphs on 9 vertices

1900 to 1999

• 1900 = number of primes <= 2¹⁴
• 1901 = Sophie Germain prime, centered decagonal number
• 1902 = number of symmetric plane partitions of 27
• 1903 = generalized Catalan number
• 1905 = Fermat pseudoprime
• 1907 = safe prime, balanced prime
• 1908 = coreful perfect number
• 1909 = hyperperfect number
• 1910 = number of compositions of 13 having exactly one fixed point
• 1911 = heptagonal pyramidal number
• 1912 = size of 6th maximum raising after one blind in pot-limit poker
• 1913 = super-prime, Honaker prime
• 1915 = number of nonisomorphic semigroups of order 5
• 1917 = number of partitions of 51 into pairwise relatively prime parts
• 1918 = heptagonal number
• 1919 = smallest number with reciprocal of period length 36 in base 10
• 1920 = sum of the nontriangular numbers between successive triangular numbers 120 and 136,
• 1923 = 2 × 31² + 1 = number of different 2 X 2 determinants with integer entries from 0 to 31
• 1925 = number of ways to write 24 as an orderless product of orderless sums
• 1926 = pentagonal number
• 1928 = number of distinct values taken by 2^2^...^2 (with 13 2's and parentheses inserted in all possible ways)
• 1929 = Mertens function zero, number of integer partitions of 42 whose distinct parts are connected
• 1930 = number of pairs of consecutive integers x, x+1 such that all prime factors of both x and x+1 are at most 53
• 1931 = Sophie Germain prime
• 1932 = number of partitions of 40 into prime power parts
• 1933 = centered heptagonal number, Honaker prime
• 1934 = sum of totient function for first 79 integers
• 1935 = number of edges in the join of two cycle graphs, both of order 43
• 1937 = number of chiral n-ominoes in 12-space, one cell labeled
• 1938 = Mertens function zero, number of points on surface of octahedron with edge length 22
• 1939 = 7-Knödel number
• 1940 = the Mahonian number: T(8, 9)
• 1941 = maximal number of regions obtained by joining 16 points around a circle by straight lines
• 1942 = number k for which 10k + 1, 10k + 3, 10k + 7, 10k + 9 and 10k + 13 are primes
• 1943 = largest number not the sum of distinct tetradecagonal numbers
• 1944 = 3-smooth number (2³×3⁵), Achilles number
• 1945 = number of partitions of 25 into relatively prime parts such that multiplicities of parts are also relatively prime
• 1947 = k such that 5·2^k + 1 is a prime factor of a Fermat number 2^2m + 1 for some m
• 1948 = number of strict solid partitions of 20
• 1949 = smallest prime > 44².
• 1950 = $1\cdot 2\cdot 3+4\cdot 5\cdot 6+7\cdot 8\cdot 9+10\cdot 11\cdot 12$, largest number not the sum of distinct pentadecagonal numbers
• 1951 = cuban prime
• 1952 = number of covers of {1, 2, 3, 4}
• 1953 = hexagonal prism number, 62nd triangular number
• 1955 = number of partitions of 25 with at least one distinct part
• 1956 = nonagonal number
• 1957 = $\sum _{k=0}^{6}{\frac {6!}{k!}}$ = total number of ordered k-tuples (k=0,1,2,3,4,5,6) of distinct elements from an 6-element set
• 1958 = number of partitions of 25
• 1960 = number of parts in all partitions of 33 into distinct parts
• 1961 = number of lattice points inside a circle of radius 25
• 1962 = number of edges in the join of the complete graph K₃₆ and the cycle graph C₃₆
• 1963! - 1 is prime
• 1964 = number of linear forests of planted planar trees with 8 nodes
• 1965 = total number of parts in all partitions of 17
• 1966 = sum of totient function for first 80 integers
• 1967 = least edge-length of a square dissectable into at least 30 squares in the Mrs. Perkins's quilt problem
• σ(1968) = σ(1967) + σ(1966)
• 1969 = Only value less than four million for which a "mod-ification" of the standard Ackermann Function does not stabilize
• 1970 = number of compositions of two types of 9 having no even parts
• 1972 = n such that ${\frac {n^{37}-1}{n-1}}$ is prime
• 1973 = Sophie Germain prime, Leonardo prime
• 1974 = number of binary vectors of length 17 containing no singletons
• 1975 = number of partitions of 28 with nonnegative rank
• 1976 = octagonal number
• 1977 = number of non-isomorphic multiset partitions of weight 9 with no singletons
• 1979 = number of squares between 45² and 45⁴, smallest number that is the sum of 4 positive cubes in at least 4 ways
• 1980 = pronic number, highly abundant number with a greater sum of proper divisors than all smaller numbers
• 1981 = pinwheel number, central polygonal number
• 1982 = maximal number of regions the plane is divided into by drawing 45 circles, a number with the property that 3¹⁹⁸² - 1982 is prime
• 1984 = 11111000000 in binary, nonunitary perfect number, see also: 1984 (disambiguation)
• 1985 = centered square number
• 1986 = number of ways to write 25 as an orderless product of orderless sums
• 1987 = 300th prime number
• 1988 = sum of the first 33 primes, sum of the first 51 composite numbers
• 1989 = number of balanced primes less than 100,000, number of 9-step mappings with 4 inputs
• 1990 = Stella octangula number
• 1991 = 11 × 181, the 46th Gullwing number, palindromic composite number with only palindromic prime factors
• 1992 = number of nonisomorphic sets of nonempty subsets of a 4-set
• 1993 = a number with the property that 4¹⁹⁹³ - 3¹⁹⁹³ is prime, number of partitions of 30 into a prime number of parts
• 1995 = number of unlabeled graphs on 9 vertices with independence number 6
• 1997 = $\sum _{k=1}^{21}{k\cdot \phi (k)}$
• 1999 = centered triangular number, number of regular forms in a myriagram.

Prime numbers

There are 135 prime numbers between 1000 and 2000:

1009, 1013, 1019, 1021, 1031, 1033, 1039, 1049, 1051, 1061, 1063, 1069, 1087, 1091, 1093, 1097, 1103, 1109, 1117, 1123, 1129, 1151, 1153, 1163, 1171, 1181, 1187, 1193, 1201, 1213, 1217, 1223, 1229, 1231, 1237, 1249, 1259, 1277, 1279, 1283, 1289, 1291, 1297, 1301, 1303, 1307, 1319, 1321, 1327, 1361, 1367, 1373, 1381, 1399, 1409, 1423, 1427, 1429, 1433, 1439, 1447, 1451, 1453, 1459, 1471, 1481, 1483, 1487, 1489, 1493, 1499, 1511, 1523, 1531, 1543, 1549, 1553, 1559, 1567, 1571, 1579, 1583, 1597, 1601, 1607, 1609, 1613, 1619, 1621, 1627, 1637, 1657, 1663, 1667, 1669, 1693, 1697, 1699, 1709, 1721, 1723, 1733, 1741, 1747, 1753, 1759, 1777, 1783, 1787, 1789, 1801, 1811, 1823, 1831, 1847, 1861, 1867, 1871, 1873, 1877, 1879, 1889, 1901, 1907, 1913, 1931, 1933, 1949, 1951, 1973, 1979, 1987, 1993, 1997, 1999