OFFSET
0,2
FORMULA
G.f. A(x) satisfies: A(x) = 1 + 7 * x * A(x/(1 - x)) / (1 - x)^2.
MATHEMATICA
a[0] = 1; a[n_] := a[n] = 7 Sum[Binomial[n, k] a[k - 1], {k, 1, n}]; Table[a[n], {n, 0, 20}]
nmax = 20; A[_] = 0; Do[A[x_] = 1 + 7 x A[x/(1 - x)]/(1 - x)^2 + O[x]^(nmax + 1) // Normal, nmax + 1]; CoefficientList[A[x], x]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jun 07 2021
STATUS
approved