OFFSET
0,2
LINKS
Winston de Greef, Table of n, a(n) for n = 0..1067
FORMULA
a(n) = (-1)^(n-1) * Sum_{k=0..n} binomial(3*k-1,k) * binomial(n+k-2,n-k)/(3*k-1).
PROG
(PARI) a(n) = (-1)^(n-1)*sum(k=0, n, binomial(3*k-1, k)*binomial(n+k-2, n-k)/(3*k-1));
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Oct 07 2023
STATUS
approved