OFFSET
0,3
FORMULA
G.f.: Sum_{k>=0} (k^2 * x)^k/(1 + k^2 * x).
a(n) ~ 1/(1 + exp(-2)) * n^(2*n). - Vaclav Kotesovec, Dec 10 2021
MATHEMATICA
Join[{1}, Table[Sum[(-1)^(n-k) k^(2n), {k, 0, n}], {n, 20}]] (* Harvey P. Dale, Nov 19 2023 *)
PROG
(PARI) a(n) = sum(k=0, n, (-1)^(n-k)*k^(2*n));
(PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=0, N, (k^2*x)^k/(1+k^2*x)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 04 2021
STATUS
approved