OFFSET
1,3
FORMULA
a(1) = 1; a(n) = (n-1)! * ((-1)^n + Sum_{d|n, 1 < d < n} d * (-d!)^(-n/d) * a(d)).
MATHEMATICA
nn = 22; f[x_] := Product[(1 + x^n/n!)^a[n], {n, 1, nn}]; sol = SolveAlways[0 == Series[f[x] - Exp[x], {x, 0, nn}], x]; Table[a[n], {n, 1, nn}] /. sol // Flatten
a[1] = 1; a[n_] := a[n] = (n - 1)! ((-1)^n + Sum[d (-d!)^(-n/d) a[d], {d, Divisors[n] ~ Complement ~ {1, n}}]); Table[a[n], {n, 1, 22}]
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, May 14 2022
STATUS
approved