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