OFFSET
0,2
FORMULA
a(n) = (1/(n+1)) * Sum_{k=0..floor(n/4)} (-1)^k * binomial(n+k,k) * binomial(3*n-3*k+1,n-4*k).
PROG
(PARI) a(n) = sum(k=0, n\4, (-1)^k*binomial(n+k, k)*binomial(3*n-3*k+1, n-4*k))/(n+1);
(PARI) my(x='x+O('x^30)); Vec(serreverse(x*(1-x)*(1-x+x^4))/x) \\ Michel Marcus, Jan 10 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jan 10 2024
STATUS
approved