A015761 Numbers k such that phi(k) | sigma_3(k).

1, 2, 3, 6, 12, 14, 15, 30, 35, 38, 42, 54, 56, 70, 78, 87, 95, 105, 114, 126, 135, 140, 147, 168, 174, 182, 190, 209, 210, 215, 216, 222, 248, 258, 264, 270, 285, 294, 297, 315, 357, 418, 420, 430, 455, 456, 540, 546, 551, 570, 594, 609, 616, 627

Offset: 1

Author

Robert G. Wilson v

Keywords

• nonn

Comments

sigma_3(k) is the sum of the cubes of the divisors of k (A001158).

Links

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

Crossrefs

Cf. A000010, A001158.

Programs

Mathematica

Select[Range[630], Divisible[DivisorSigma[3, #], EulerPhi[#]] &] (* Amiram Eldar, Jun 23 2019 *)

PARI

isok(k) = (sigma(k, 3) % eulerphi(k)) == 0; \\ Michel Marcus, Jun 23 2019