OFFSET
0,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..1000
FORMULA
a(n) = Sum_{k=1..n} 9^gcd(n,k). - Ilya Gutkovskiy, Apr 16 2021
PROG
(PARI) a(n) = if(n==0, 0, sumdiv(n, d, eulerphi(d)*9^(n/d))); \\ Altug Alkan, Mar 16 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Apr 16 2000
STATUS
approved