OFFSET
0,3
FORMULA
a(n) = Sum_{k=0..n} (-1)^(n-k) * k^(3*n-2*k).
MATHEMATICA
a[n_] := Sum[If[k == 3*n - 2*k == 0, 1, (-1)^(n - k) * k^(3*n - 2*k)], {k, 0, n}]; Array[a, 17, 0] (* Amiram Eldar, Dec 04 2021 *)
PROG
(PARI) a(n, t=3) = sum(k=0, n, (-k^t)^(n-k)*k^k);
(PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=0, N, (k*x)^k/(1+k^3*x)))
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Dec 03 2021
STATUS
approved