OFFSET
0,2
FORMULA
a(n) = [x^n] 1/((1-x-x^2) * (1-x)^(3*n)).
a(n) ~ 2^(8*n + 5/2) / (11 * sqrt(Pi*n) * 3^(3*n - 1/2)). - Vaclav Kotesovec, Apr 05 2024
PROG
(PARI) a(n) = sum(k=0, n\2, binomial(4*n-k, n-2*k));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 05 2024
STATUS
approved