A046678 Number of divisors of n and sum of divisors of n are relatively prime.

1, 2, 4, 8, 9, 16, 25, 36, 64, 81, 100, 121, 128, 144, 162, 225, 256, 289, 324, 400, 484, 512, 529, 576, 625, 729, 841, 900, 1024, 1089, 1156, 1250, 1296, 1458, 1600, 1681, 1936, 2025, 2116, 2209, 2304, 2401, 2500, 2601, 2809, 3025, 3364, 3481

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. A000005, A000203, A028982, A046679, A046680, A046681, A046683, A046685.

Programs

Mathematica

Select[Range[3490], CoprimeQ[DivisorSigma[1, #], DivisorSigma[0, #]] &] (* Jayanta Basu, Jun 27 2013 *)

PARI

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