OFFSET
0,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..1000
FORMULA
a(n) = [x^n] 1/((1-x^3) * (1-x)^(3*n+1)).
a(n) = Sum_{k=0..n} (-3)^k * binomial(4*n+k+3,n-k).
PROG
(PARI) a(n) = sum(k=0, n\3, binomial(4*n-3*k, n-3*k));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Nov 13 2025
STATUS
approved