OFFSET
1,3
FORMULA
a(1) = 1; a(n+1) = Sum_{k=1..n} binomial(n,k) * Sum_{d|k} a(d).
MATHEMATICA
terms = 25; A[_] = 0; Do[A[x_] = x (1 + 1/(1 - x) Sum[A[x^k/(1 - x)^k], {k, 1, terms}]) + O[x]^(terms + 1) // Normal, terms + 1]; Rest[CoefficientList[A[x], x]]
a[n_] := a[n] = Sum[Binomial[n - 1, k] Sum[a[d], {d, Divisors[k]}], {k, 1, n - 1}]; a[1] = 1; Table[a[n], {n, 1, 25}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, May 09 2019
STATUS
approved