OFFSET
0,3
FORMULA
a(n) = [x^n] 1/(1 - x - (n*x)^2).
a(n) ~ (exp(1/2) + (-1)^n*exp(-1/2)) * n^n / 2. - Vaclav Kotesovec, Jan 09 2024
MATHEMATICA
Table[Hypergeometric2F1[1/2 - n/2, -n/2, -n, -4*n^2], {n, 0, 20}] (* Vaclav Kotesovec, Jan 09 2024 *)
PROG
(PARI) a(n) = sum(k=0, n\2, n^(2*k)*binomial(n-k, k));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Jan 09 2024
STATUS
approved