20,000

20,000 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 10020100 = sum of the first 200 natural numbers 20160 = 23rd highly composite number; the smallest order belonging to two non-isomorphic simple groups: the alternating group A₈ and the Chevalley group A₂20161 = the largest integer that cannot be expressed as a sum of two abundant numbers20230 = pentagonal pyramidal number20412 = Leyland number: 9³ + 3⁹20540 = square pyramidal number20569 = tetranacci number20593 = unique prime in base 1220597 = k such that the sum of the squares of the first k primes is divisible by k.20736 = 144² = 12⁴, 10000₁₂, palindromic in base 15, also called a dozen great-gross in some duodecimal nomenclature.20793 = little Schroeder number20871 = The number of weeks in exactly 400 years in the Gregorian calendar20903 = first prime of form 120k + 23 that is not a full reptend prime

21000 to 21999

21025 = 145², palindromic in base 12 21147 = Bell number21181 = the least of five remaining Seventeen or Bust numbers in the Sierpiński problem21209 = number of reduced trees with 23 nodes21637 = number of partitions of 3721856 = octahedral number21943 = Friedman prime21952 = 28³21978 = reverses when multiplied by 4: 4 × 21978 = 87912

22000 to 22999

22050 = pentagonal pyramidal number22140 = square pyramidal number22222 = repdigit, Kaprekar number: 22222² = 493817284, 4938 + 17284 = 2222222447 = cuban prime22527 = Woodall number: 11 × 2¹¹ − 122621 = repunit prime in base 1222699 = one of five remaining Seventeen or Bust numbers in the Sierpiński problem

23000 to 23999

23000 = number of primes.23401 = Leyland number: 6⁵ + 5⁶23409 = 153², sum of the cubes of the first 17 positive integers23497 = cuban prime23821 = square pyramidal number23833 = Padovan prime23969 = octahedral number23976 = pentagonal pyramidal number

24000 to 24999

24000 = number of primitive polynomials of degree 20 over GF24211 = Zeisel number24336 = 156², palindromic in base 5: 1234321₅24389 = 29³24571 = cuban prime24631 = Wedderburn–Etherington prime24649 = 157², palindromic in base 12: 12321₁₂24737 = one of five remaining Seventeen or Bust numbers in the Sierpinski problem24742 = 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 digit25085 = Zeisel number25117 = cuban prime25200 = 224th triangular number, 24th highly composite number, smallest number with exactly 90 factors25205 = largest number whose factorial is less than 10¹⁰⁰⁰⁰⁰25482 = number of 21-bead necklaces where complements are equivalent25585 = square pyramidal number25724 = Fine number25920 = smallest number with exactly 70 factors

26000 to 26999

26015 = number of partitions of 3826214 = octahedral number26227 = cuban prime26272 = number of 20-bead binary necklaces with beads of 2 colors where the colors may be swapped but turning over is not allowed26861 = 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 bias26896 = 164², palindromic in base 9: 40804₉

27000 to 27999

27000 = 30³27405 = heptagonal number, hexadecagonal number, 48-gonal number, 80-gonal number, smallest integer that is polygonal in exactly 10 ways.27434 = square pyramidal number27559 = Zeisel number27594 = number of primitive polynomials of degree 19 over GF27648 = 1¹ × 2² × 3³ × 4⁴27653 = Friedman prime27720 = 25th highly composite number; smallest number divisible by the numbers from 1 to 12 27846 = harmonic divisor number27889 = 167²

28000 to 28999

28158 = pentagonal pyramidal number28374 = smallest integer to start a run of six consecutive integers with the same number of divisors28393 = unique prime in base 1328547 = Friedman prime28559 = nice Friedman prime28561 = 169² = 13⁴ = 119² + 120², number that is simultaneously a square number and a centered square number, palindromic in base 12: 14641₁₂28595 = octahedral number28657 = Fibonacci prime, Markov prime28900 = 170², palindromic in base 13: 10201₁₃

29000 to 29999

29241 = 171², sum of the cubes of the first 18 positive integers29341 = Carmichael number29370 = square pyramidal number29527 = Friedman prime29531 = Friedman prime29601 = number of planar partitions of 1829791 = 31³

Primes

There are 983 prime numbers between 20000 and 30000.