OFFSET
0,2
FORMULA
a(n) = (1/(n+1)) * Sum_{k=0..floor(n/4)} binomial(n+k,k) * binomial(3*n-2*k+1,n-4*k).
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(serreverse(x*((1-x)^2-x^4))/x)
(PARI) a(n) = sum(k=0, n\4, binomial(n+k, k)*binomial(3*n-2*k+1, n-4*k))/(n+1);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jan 15 2024
STATUS
approved