20,000 (twenty thousand) is the natural number that comes after 19,999 and before 20,001. Selected numbers in the range 20001–29999
20001 to 20999 20002 = number of surface-points of a tetrahedron with edge-length 100 20067 = The smallest uninteresting number 20100 = sum of the first 200 natural numbers (hence the 200th triangular number) 20160 = 23rd highly composite number; the smallest order belonging to two non-isomorphic simple groups: the alternating group A8 and the Chevalley group A2(4) 20161 = the largest integer that cannot be expressed as a sum of two abundant numbers 20230 = pentagonal pyramidal number 20412 = Leyland number: 93 + 39 20540 = square pyramidal number 20569 = tetranacci number 20593 = unique prime in base 12 20736 = 1442 = 124, 1000012, palindromic in base 15 (622615), also called a dozen great-gross in some duodecimal nomenclature. 20793 = little Schroeder number 20871 = The number of weeks in exactly 400 years in the Gregorian calendar 20903 = first prime of form 120k + 23 that is not a full reptend prime
21000 to 21999 21025 = 1452, palindromic in base 12 (1020112) 21147 = Bell number 21181 = the least of five remaining Seventeen or Bust numbers in the Sierpiński problem 21209 = number of reduced trees with 23 nodes 21637 = number of partitions of 37 21856 = octahedral number 21943 = Friedman prime
22000 to 22999 22050 = pentagonal pyramidal number 22140 = square pyramidal number 22222 = repdigit, Kaprekar number: 222222 = 493817284, 4938 + 17284 = 22222 22447 = cuban prime 22527 = Woodall number: 11 × 211 − 1 22621 = repunit prime in base 12 22699 = one of five remaining Seventeen or Bust numbers in the Sierpiński problem
23000 to 23999 23000 = number of primes . 23401 = Leyland number: 65 + 56 23409 = 1532, sum of the cubes of the first 17 positive integers 23497 = cuban prime 23821 = square pyramidal number 23833 = Padovan prime 23969 = octahedral number 23976 = pentagonal pyramidal number 23982 = year in which the Gregorian calendar will begin to differ from the tropical year by one week.
24000 to 24999 24000 = number of primitive polynomials of degree 20 over GF(2) 24211 = Zeisel number 24336 = 1562, palindromic in base 5: 12343215 24389 = 293 24571 = cuban prime 24631 = Wedderburn–Etherington prime 24649 = 1572, palindromic in base 12: 1232112 24737 = one of five remaining Seventeen or Bust numbers in the Sierpinski problem 24742 = number of signed trees with 10 nodes
25000 to 25999 25011 = the smallest composite number, ending in 1, 3, 7, or 9, that in base 10 remains composite after any insertion of a digit 25085 = Zeisel number 25117 = cuban prime 25200 = 224th triangular number, 24th highly composite number, smallest number with exactly 90 factors 25205 = largest number whose factorial is less than 10100000 25482 = number of 21-bead necklaces (turning over is allowed) where complements are equivalent 25585 = square pyramidal number 25724 = Fine number 25920 = smallest number with exactly 70 factors
26000 to 26999 26015 = number of partitions of 38 26214 = octahedral number 26227 = cuban prime 26272 = number of 20-bead binary necklaces with beads of 2 colors where the colors may be swapped but turning over is not allowed 26861 = smallest number for which there are more primes of the form 4k + 1 than of the form 4k + 3 up to the number, against Chebyshev's bias 26896 = 1642, palindromic in base 9: 408049 26955 = amount of SI days in the average human lifetime of 73.8 calendar years.
27000 to 27999 27405 = heptagonal number, hexadecagonal number, 48-gonal number, 80-gonal number, smallest integer that is polygonal in exactly 10 ways. 27434 = square pyramidal number 27559 = Zeisel number 27594 = number of primitive polynomials of degree 19 over GF(2) 27648 = 11 × 22 × 33 × 44 27653 = Friedman prime 27720 = 25th highly composite number; smallest number divisible by the numbers from 1 to 12 (there is no smaller number divisible by the numbers from 1 to 11 since any number divisible by 3 and 4 must be divisible by 12) 27846 = harmonic divisor number
28000 to 28999 28158 = pentagonal pyramidal number 28374 = smallest integer to start a run of six consecutive integers with the same number of divisors 28393 = unique prime in base 13 28547 = Friedman prime 28559 = nice Friedman prime 28561 = 1692 = 134 = 1192 + 1202, number that is simultaneously a square number and a centered square number, palindromic in base 12: 1464112 28595 = octahedral number 28657 = Fibonacci prime, Markov prime 28900 = 1702, palindromic in base 13: 1020113
29000 to 29999 29241 = 1712, sum of the cubes of the first 18 positive integers 29341 = Carmichael number 29370 = square pyramidal number 29527 = Friedman prime 29531 = Friedman prime 29601 = number of planar partitions of 18
Primes There are 983 prime numbers between 20000 and 30000.
References