A046680 Numbers k such that the number of divisors of k and sum of cubes of divisors of k are relatively prime.

1, 2, 4, 8, 9, 16, 25, 36, 81, 100, 121, 128, 144, 162, 225, 256, 289, 324, 400, 484, 512, 529, 625, 729, 841, 900, 1024, 1089, 1156, 1250, 1296, 1458, 1681, 1936, 2025, 2116, 2209, 2304, 2401, 2500, 2601, 2809, 2916, 3025, 3364, 3481, 3600, 4096, 4356, 4624

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, A046679, A046681, A046683, A046685.

Programs

Mathematica

Select[Range[5000], CoprimeQ[DivisorSigma[0, #], DivisorSigma[3, #]] &] (* Amiram Eldar, Aug 08 2019 *)

PARI

isok(n) = gcd(numdiv(n), sigma(n, 3)) == 1; \\ Michel Marcus, Sep 24 2019