OFFSET
0,2
FORMULA
a(n) = [x^n] 1/(1 - x - x/(1 - x)^2)^n.
PROG
(PARI) a(n) = sum(k=0, n, binomial(n+k-1, k)*binomial(2*n+2*k-1, n-k));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Nov 27 2024
STATUS
approved