OFFSET
1,2
FORMULA
G.f. A(x) satisfies: A(x) = x * (1 / (1 - x) + Sum_{k>=1} mu(k) * A(x^k)).
MATHEMATICA
a[1] = 1; a[n_] := a[n] = 1 + Sum[MoebiusMu[(n - 1)/d] a[d], {d, Divisors[n - 1]}]; Table[a[n], {n, 1, 70}]
nmax = 70; A[_] = 0; Do[A[x_] = x (1/(1 - x) + Sum[MoebiusMu[k] A[x^k], {k, 1, nmax}]) + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x] // Rest
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Jul 05 2021
STATUS
approved