OFFSET
1,2
FORMULA
a(1) = 1; a(n) = Sum_{d|n, d<n} 2^(n/d-1)*a(d).
a(n) ~ 2^(n-1). - Vaclav Kotesovec, Oct 16 2019
MATHEMATICA
terms = 35; A[_] = 0; Do[A[x_] = x + Sum[2^(k - 1) A[x^k], {k, 2, terms}] + O[x]^(terms + 1) //Normal, terms + 1]; Rest[CoefficientList[A[x], x]]
a[n_] := If[n == 1, n, Sum[If[d < n, 2^(n/d - 1) a[d], 0], {d, Divisors[n]}]]; Table[a[n], {n, 1, 35}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, May 11 2019
STATUS
approved