A054614 a(n) = Sum_{d|n} phi(d)*7^(n/d).

0, 7, 56, 357, 2464, 16835, 118104, 823585, 5767328, 40354335, 282492280, 1977326813, 13841410464, 96889010491, 678223896728, 4747561544985, 33232936339456, 232630513987319, 1628413638500376, 11398895185373269

Offset: 0

Author

N. J. A. Sloane, Apr 16 2000

Keywords

• nonn

Links

• Seiichi Manyama, Table of n, a(n) for n = 0..1000

Crossrefs

Column k=7 of A185651.

Cf. A054626.

Programs

PARI

a(n) = sumdiv(n, d, eulerphi(d)*7^(n/d)); \\ Michel Marcus, Jul 11 2021

Formula

a(n) = Sum_{k=1..n} 7^gcd(n,k). - Ilya Gutkovskiy, Apr 16 2021