OFFSET
0,3
FORMULA
E.g.f.: 1 / (1 + exp(x) * x * (1 + x)).
E.g.f.: 1 / (1 + Sum_{k>=1} k^2 * x^k / k!).
MATHEMATICA
a[0] = 1; a[n_] := a[n] = -Sum[Binomial[n, k] k^2 a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 21}]
nmax = 21; CoefficientList[Series[1/(1 + Exp[x] x (1 + x)), {x, 0, nmax}], x] Range[0, nmax]!
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Jan 26 2021
STATUS
approved