OFFSET
0,5
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..240
FORMULA
G.f.: Sum_{k>=0} (k^2 * x)^(2 * k) / (1 - k^2 * x).
a(n) ~ exp(3 + (-1)^n) * (n/2)^(2*n) / (exp(4) - 1). - Vaclav Kotesovec, Apr 14 2022
MATHEMATICA
a[0] = 1; a[n_] := Sum[k^(2*n), {k, 0, Floor[n/2]}]; Array[a, 17, 0] (* Amiram Eldar, Apr 13 2022 *)
PROG
(PARI) a(n) = sum(k=0, n\2, k^(2*n));
(PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=0, N, (k^2*x)^(2*k)/(1-k^2*x)))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Apr 13 2022
STATUS
approved