A046679 Numbers k such that the number of divisors of k and sum of squares of divisors of k are relatively prime.

1, 2, 8, 9, 16, 18, 64, 72, 81, 128, 144, 625, 729, 1024, 1152, 1296, 1458, 2401, 4096, 5184, 5625, 5832, 6561, 8192, 9216, 10000, 11664, 13122, 15625, 21609, 28561, 31250, 32768, 38416, 40000, 46656, 50625, 52488, 59049, 65536, 83521, 90000

Offset: 1

Author

Labos Elemer

Keywords

• nonn

Comments

It can be shown that this is a subsequence of A028982.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A028982, A046678, A046680, A046681, A046683, A046685.

Programs

Mathematica

Select[Range[91000],CoprimeQ[DivisorSigma[0,#], DivisorSigma[2,#]]&] (* Harvey P. Dale, May 11 2011 *)

PARI

isok(n) = gcd(sigma(n, 2), numdiv(n)) == 1; \\ Michel Marcus, Sep 24 2019

Extensions

a(1)=1 added by Amiram Eldar, Sep 24 2019