OFFSET
0,4
FORMULA
a(n) = Sum_{k=0..floor(n/2)} binomial(3*k,n-2*k) * binomial(4*k,k)/(3*k+1).
PROG
(PARI) a(n) = sum(k=0, n\2, binomial(3*k, n-2*k)*binomial(4*k, k)/(3*k+1));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Oct 14 2023
STATUS
approved