OFFSET
0,3
FORMULA
a(n) = Sum_{k=0..n} (-1)^(n-k) * binomial(6*n-k+1,k) * binomial(n-1,n-k)/(6*n-k+1).
PROG
(PARI) a(n) = sum(k=0, n, (-1)^(n-k)*binomial(6*n-k+1, k)*binomial(n-1, n-k)/(6*n-k+1));
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Aug 27 2023
STATUS
approved