OFFSET
0,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..1000
FORMULA
a(n) = Sum_{k=1..n} 7^gcd(n,k). - Ilya Gutkovskiy, Apr 16 2021
PROG
(PARI) a(n) = sumdiv(n, d, eulerphi(d)*7^(n/d)); \\ Michel Marcus, Jul 11 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Apr 16 2000
STATUS
approved