OFFSET
0,4
FORMULA
a(n) = (1/n) * Sum_{k=0..n-1} (-1)^k * binomial(n,k) * binomial(n+3*k,n-1-k) for n > 0.
PROG
(PARI) a(n) = if(n==0, 1, sum(k=0, n-1, (-1)^k*binomial(n, k)*binomial(n+3*k, n-1-k))/n);
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Aug 05 2023
STATUS
approved