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 A137484 Numbers with 21 divisors. 6
 576, 1600, 2916, 3136, 7744, 10816, 18225, 18496, 23104, 33856, 35721, 53824, 61504, 62500, 87616, 88209, 107584, 118336, 123201, 140625, 141376, 179776, 210681, 222784, 238144, 263169, 287296, 322624, 341056, 385641, 399424, 440896 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Maple implementation: see A030513. Numbers of the form p^20 or p^2*q^6 (A189990) where p and q are distinct primes. - R. J. Mathar, Mar 01 2010 LINKS T. D. Noe, Table of n, a(n) for n = 1..1000 FORMULA A000005(a(n))=21. MATHEMATICA Select[Range[450000], DivisorSigma[0, #]==21&] (* Vladimir Joseph Stephan Orlovsky, May 03 2011 *) PROG (PARI) is(n)=numdiv(n)==21 \\ Charles R Greathouse IV, Jun 19 2016 CROSSREFS Cf. A030513-A030516, A030626, A030627, A030634-A030638, A005179, A003680, A096932, A061286, A061283. Sequence in context: A235181 A268773 A250789 * A189990 A064254 A281242 Adjacent sequences:  A137481 A137482 A137483 * A137485 A137486 A137487 KEYWORD nonn AUTHOR R. J. Mathar, Apr 22 2008 STATUS approved

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Last modified December 18 23:46 EST 2018. Contains 318245 sequences. (Running on oeis4.)