OFFSET
0,3
FORMULA
G.f. A(x) satisfies: A(x) = 1 + x + x^2 * (A(x) + (1/(1 - x)) * A(x/(1 - x))).
MATHEMATICA
a[0] = a[1] = 1; a[n_] := a[n] = a[n - 2] + Sum[Binomial[n - 2, k] a[k], {k, 0, n - 2}]; Table[a[n], {n, 0, 27}]
nmax = 27; A[_] = 0; Do[A[x_] = 1 + x + x^2 (A[x] + (1/(1 - x)) A[x/(1 - x)]) + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jul 04 2020
STATUS
approved