OFFSET
0,3
FORMULA
a(n) = Sum_{k=0..floor(n/4)} binomial(n-3*k,k) * binomial(2*n-5*k+1,n-3*k)/(2*n-5*k+1).
PROG
(PARI) a(n) = sum(k=0, n\4, binomial(n-3*k, k)*binomial(2*n-5*k+1, n-3*k)/(2*n-5*k+1));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Aug 30 2023
STATUS
approved