OFFSET
0,4
FORMULA
a(n) = Sum_{k=0..floor(n/3)} binomial(n-k,2*k) * binomial(3*k,k) / (2*k+1).
PROG
(PARI) a(n) = sum(k=0, n\3, binomial(n-k, 2*k)*binomial(3*k, k)/(2*k+1));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Jul 29 2023
STATUS
approved