A054612 a(n) = Sum_{d|n} phi(d)*5^(n/d).

0, 5, 30, 135, 660, 3145, 15810, 78155, 391320, 1953405, 9768870, 48828175, 244157820, 1220703185, 6103593930, 30517584915, 152588282640, 762939453205, 3814699250430, 19073486328215, 95367441415140, 476837158360185, 2384185839844050, 11920928955078235, 59604645020345640

Offset: 0

Author

N. J. A. Sloane, Apr 16 2000

Keywords

• nonn
• changed

Links

• Seiichi Manyama, Table of n, a(n) for n = 0..1430

Crossrefs

Column k=5 of A185651.

Cf. A001869.

Programs

Mathematica

a[n_]:= Sum[5^GCD[n,k],{k,n}]; Array[a,30,0] (* Stefano Spezia, Sep 02 2025 *)

PARI

a(n) = if (n, sumdiv(n, d, eulerphi(d)*5^(n/d)), 0); \\ Michel Marcus, Apr 16 2021

Formula

a(n) = Sum_{k=1..n} 5^gcd(n,k). - Ilya Gutkovskiy, Apr 16 2021