OFFSET
1,2
FORMULA
a(n) = A060170(n)/3. - Hugo Pfoertner, Jul 24 2021
MATHEMATICA
Table[(1/(3 n)) Sum[MoebiusMu[n/d] Binomial[3 d, d], {d, Divisors[n]}], {n, 24}]
PROG
(PARI) a(n) = sumdiv(n, d, moebius(n/d)*binomial(3*d, d))/(3*n); \\ Michel Marcus, Jul 24 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jul 24 2021
STATUS
approved