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

1,2

Comments

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

Links

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

Mathematica

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

Prog

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

Crossrefs

Cf. A028982, A046678, A046679, A046681, A046683, A046685.

Sequence in context: A348825 A046678 A330606 * A331992 A113570 A065391

Adjacent sequences: A046677 A046678 A046679 * A046681 A046682 A046683

Keyword

nonn

Author

Labos Elemer

Status

approved