OFFSET
1,3
COMMENTS
a(2^k)=1, a(3^k)=5, a(5^k)=119, a(6*2^i*3^j)=713, a(7^k)=5039, a(10*2^i*5^j)=3628679, etc. - Robert G. Wilson v, Nov 12 2004
FORMULA
G.f.: Sum_{k>=1} mu(k)*k!*x^k/(1 - x^k). - Ilya Gutkovskiy, Feb 19 2017
MATHEMATICA
f[n_] := Block[{k = Divisors[n]}, Plus @@ (k!MoebiusMu[k])]; Table[ f[n], {n, 25}] (* Robert G. Wilson v, Nov 12 2004 *)
PROG
(PARI) a(n) = sumdiv(n, d, d!*moebius(d)); \\ Michel Marcus, Feb 19 2017
CROSSREFS
KEYWORD
sign
AUTHOR
Leroy Quet, Nov 09 2004
EXTENSIONS
More terms from Robert G. Wilson v, Nov 12 2004
STATUS
approved