20,000

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 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 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), 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