OFFSET
0,2
FORMULA
a(n) = (1/(n+1)) * Sum_{k=0..n} binomial(4*n+k+3,k) * binomial(3*(n+1),n-k).
PROG
(PARI) a(n) = sum(k=0, n, binomial(4*n+k+3, k)*binomial(3*(n+1), n-k))/(n+1);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Sep 20 2023
STATUS
approved