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