20,000

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List of numbers Integers ← 0 10k 20k 30k 40k 50k 60k 70k 80k 90k →
Cardinal	twenty thousand
Ordinal	20000th (twenty thousandth)
Factorization	25 × 54
Greek numeral	${\stackrel {\beta }{\mathrm {M} }}$
Roman numeral	XX
Binary	1001110001000002
Ternary	10001022023
Senary	2323326
Octal	470408
Duodecimal	B6A812
Hexadecimal	4E2016

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

20,000 is a round number, and is also in the title of Jules Verne's novel Twenty Thousand Leagues Under the Sea.

Selected numbers in the range 20001–29999

20001 to 20999

• 20002 = number of surface-points of a tetrahedron with edge-length 100
• 20100 = sum of the first 200 natural numbers (hence a triangular number)
• 20160 = 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
• 20597 = 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 (6226₁₅)
• 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
• 21856 = octahedral number
• 21943 = Friedman prime
• 21952 = 28³
• 21978 = reverses when multiplied by 4: 4 × 21978 = 87912

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 $\leq 2^{18}$.
• 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

24000 to 24999

• 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

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 = highly composite number
• 25205 = largest number whose factorial is less than 10¹⁰⁰⁰⁰⁰
• 25585 = square pyramidal number
• 25724 = Fine number

26000 to 26999

• 26214 = octahedral number
• 26227 = cuban prime
• 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

27000 to 27999

• 27000 = 30³
• 27434 = square pyramidal number
• 27559 = Zeisel number
• 27648 = 1¹ × 2² × 3³ × 4⁴
• 27653 = Friedman prime
• 27720 = highly composite number; smallest number divisible by the numbers 1 to 12 (there is no smaller number divisible by the numbers 1 to 11 since any number divisible by 4 and 3 must be divisible by 12, since 4×3=12)
• 27846 = harmonic divisor number
• 27889 = 167²

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
• 29791 = 31³

There are 983 prime numbers between 20000 and 30000.