OFFSET
0,3
FORMULA
a(n) = Sum_{k=0..n} (-k^2)^(n-k) * k^2.
MATHEMATICA
a[n_] := Sum[If[k == n - k == 0, 1, (-k^2)^(n - k)] * k^2, {k, 0, n}]; Array[a, 21, 0] (* Amiram Eldar, Dec 03 2021 *)
PROG
(PARI) a(n, s=2, t=2) = sum(k=0, n, (-k^t)^(n-k)*k^s);
(PARI) my(N=40, x='x+O('x^N)); concat(0, Vec(sum(k=0, N, k^2*x^k/(1+k^2*x))))
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Dec 02 2021
STATUS
approved