OFFSET
0,3
FORMULA
G.f. A(x) satisfies: A(x) = 1 + 2 * x^2 * A(x^2) + 3 * x^3 * A(x^3) + 4 * x^4 * A(x^4) + ...
MATHEMATICA
a[0] = 1; a[n_] := a[n] = n DivisorSum[n, a[# - 1]/# &, # < n &]; Table[a[n], {n, 0, 60}]
nmax = 60; A[_] = 0; Do[A[x_] = 1 + Sum[k x^k A[x^k], {k, 2, nmax}] + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Nov 06 2020
STATUS
approved