A046681 Numbers k such that the number of divisors of k and sum of 4th powers of divisors of k are relatively prime.

1, 2, 8, 9, 18, 64, 72, 128, 625, 729, 1024, 1152, 1250, 1458, 4096, 5000, 5625, 5832, 6561, 8192, 9216, 11250, 13122, 15625, 31250, 32768, 40000, 45000, 46656, 52488, 59049, 65536, 80000, 93312, 117649, 118098, 125000, 235298, 262144, 294912

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..5000

Crossrefs

Cf. A028982, A046678, A046679, A046680, A046683, A046685.

Programs

Mathematica

Select[Range[300000],CoprimeQ[DivisorSigma[0,#],DivisorSigma[4,#]]&] (* Harvey P. Dale, May 30 2012 *)

PARI

isok(n) = gcd(sigma(n, 4), numdiv(n)) == 1; \\ Michel Marcus, Sep 24 2019