OFFSET
0,4
FORMULA
a(n) = [x^n] 1/(1 - x * (1 + x^2)^n).
PROG
(PARI) a(n) = sum(k=0, n^2\(2*n+1), binomial(n*(n-2*k), k));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 15 2024
STATUS
approved