OFFSET
1,2
MATHEMATICA
Table[(1/(7 n)) Sum[MoebiusMu[n/d] Binomial[7 d, d], {d, Divisors[n]}], {n, 20}]
PROG
(PARI) a(n) = sumdiv(n, d, moebius(n/d)*binomial(7*d, d))/(7*n); \\ Michel Marcus, Jul 24 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jul 24 2021
STATUS
approved