A055701 Numbers k such that k | sigma_7(k) - phi(k)^7.

1, 2, 10, 12, 26, 42, 172, 456, 588, 1326, 3315, 3635, 6468, 6720, 12102, 12922, 15288, 17836, 18810, 21756, 32984, 36108, 36603, 40572, 41748, 72905, 78120, 137004, 195216, 291060, 295176, 923212, 978014, 989604, 1009800, 1015768, 1069712, 1602692, 1711024

Offset: 1

Author

Robert G. Wilson v, Jun 09 2000

Keywords

• nonn

Comments

sigma_7(k) is the sum of the 7th powers of the divisors of k (A013955).

Links

• Amiram Eldar, Table of n, a(n) for n = 1..120

Crossrefs

Cf. A000010, A013955.

Programs

Mathematica

Do[If[Mod[DivisorSigma[7, n]-EulerPhi[n]^7, n]==0, Print[n]], {n, 1, 10^5}]
Select[Range[2*10^6],Divisible[DivisorSigma[7,#]-EulerPhi[#]^7,#]&] (* Harvey P. Dale, Dec 02 2016 *)

PARI

isok(n) = !((sigma(n, 7) - eulerphi(n)^7) % n); \\ Michel Marcus, Mar 02 2014

Extensions

Definition corrected and more terms from Michel Marcus, Mar 02 2014