20000 (number)

20 000 (twenty thousand) is the natural number that comes after 19,999 and before 20,001.

Selected numbers in the range 20000–29999

• 20000 – round number; also in the title of Jules Verne's novel Twenty Thousand Leagues Under the Sea
• 20081 – Motorola 68K instruction for no operation (NOP)
• 20100 – sum of the first 200 natural numbers (hence a triangular number)
• 20160 – highly composite number;^[1] 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^[2]
• 20412 – Leyland number:^[3] 9³ + 3⁹
• 20540 – square pyramidal number^[4]
• 20569 – tetranacci number^[5]
• 20736 – 12⁴, 10000₁₂, palindromic in base 15 (6226₁₅)
• 20903 – first prime of form 120k + 23 that is not a full reptend prime
• 21025 – 145², palindromic in base 12 (10201₁₂)
• 21147 – Bell number^[6]
• 21181 – the least of five remaining Seventeen or Bust numbers in the Sierpiński problem
• 21856 – octahedral number^[7]
• 21952 – 28³
• 21978 – reverses when multiplied by 4: 4 × 21978 = 87912
• 22050 – pentagonal pyramidal number^[2]
• 22140 – square pyramidal number^[4]
• 22222 – Kaprekar number:^[8] 22222² = 493817284, 4938 + 17284 = 22222
• 22447 – cuban prime^[9]
• 22527 – Woodall number: 11 × 2¹¹ − 1^[10]
• 22699 – one of five remaining Seventeen or Bust numbers in the Sierpiński problem
• 23401 – Leyland number:^[3] 6⁵ + 5⁶
• 23409 – sum of the cubes of the first 17 positive integers
• 23497 – cuban prime^[9]
• 23821 – square pyramidal number^[4]
• 23969 – octahedral number^[7]
• 23976 – pentagonal pyramidal number^[2]
• 24211 – Zeisel number^[11]
• 24336 – 156², palindromic in base 5: 1234321₅
• 24389 – 29³
• 24571 – cuban prime^[9]
• 24601 – Jean Valjean's prisoner number in Les Misérables
• 24631 – Wedderburn-Etherington number^[12]
• 24649 – 157², palindromic in base 12: 12321₁₂
• 24737 – one of five remaining Seventeen or Bust numbers in the Sierpinski problem
• 25011 – the first composite number that in base 10 remains composite after any insertion of a digit
• 25085 – Zeisel number^[11]
• 25117 – cuban prime^[9]
• 25200 – highly composite number^[1]
• 25205 – largest number whose factorial is less than 10¹⁰⁰⁰⁰⁰
• 25585 – square pyramidal number^[4]
• 26214 – octahedral number^[7]
• 26227 – cuban prime^[9]
• 26861 – smallest number below which there are more primes of the form 4k + 1 than of the form 4k + 3, against Chebyshev's bias
• 26896 – 164², palindromic in base 9: 40804₉
• 27000 – 30³
• 27434 – square pyramidal number^[4]
• 27559 – Zeisel number^[11]
• 27648 – 1¹ × 2² × 3³ × 4⁴
• 27720 – highly composite number;^[1] smallest number divisible by the numbers 1 to 12 (there is no smaller number divisible by the numbers 1 to 11)
• 27846 – harmonic divisor number^[13]
• 28158 – pentagonal pyramidal number^[2]
• 28374 – smallest integer to start a run of six consecutive integers with the same number of divisors
• 28561 – 13⁴, 119² + 120², number that is simultaneously a square number and a centered square number, palindromic in base 12: 14641₁₂
• 28595 – octahedral number^[7]
• 28657 – Fibonacci number,^[14] Markov number^[15]
• 28900 – 170², palindromic in base 13: 10201₁₃
• 29241 – sum of the cubes of the first 18 positive integers
• 29341 – Carmichael number^[16]
• 29370 – square pyramidal number^[4]
• 29791 – 31³

References