OFFSET
1,2
FORMULA
G.f. A(x) satisfies: A(x) = (1/(1 - x)) * (x + A(x^2) + A(x^3) + A(x^4) + ...).
MATHEMATICA
a[1] = 1; a[n_] := a[n] = a[n - 1] + Sum[If[d < n, a[d], 0], {d, Divisors[n]}]; Table[a[n], {n, 1, 55}]
nmax = 55; A[_] = 0; Do[A[x_] = (1/(1 - x)) (x + Sum[A[x^k], {k, 2, nmax}]) + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x] // Rest
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jun 09 2021
STATUS
approved