OFFSET
0,5
FORMULA
a(n) = Sum_{k=0..floor(n/3)} binomial(n-1,n-3*k) * binomial(3*k,k) / (2*k+1).
PROG
(PARI) a(n) = sum(k=0, n\3, binomial(n-1, n-3*k)*binomial(3*k, k)/(2*k+1));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Oct 15 2023
STATUS
approved