A030638 Numbers with 20 divisors.

240, 336, 432, 528, 560, 624, 648, 810, 816, 880, 912, 1040, 1104, 1134, 1232, 1360, 1392, 1456, 1488, 1520, 1536, 1776, 1782, 1840, 1904, 1968, 2000, 2064, 2106, 2128, 2256, 2288, 2320, 2480, 2544, 2560, 2576, 2754, 2832, 2835, 2928

Offset: 1

Author

Jeff Burch

Keywords

• nonn

Comments

Numbers of the form p^19, p*q^9 (A179692), p*q*r^4 (A179644) or p^3*q^4 (A179666), where p, q and r are distinct primes. - R. J. Mathar, Mar 01 2010

Links

• R. J. Mathar, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A030636, A030637, A137484.

Programs

Mathematica

Select[Range[20000],DivisorSigma[0,#]==20&] (* Vladimir Joseph Stephan Orlovsky, May 05 2011 *)

PARI

is(n)=numdiv(n)==20 \\ Charles R Greathouse IV, Jun 19 2016