OFFSET
0,2
FORMULA
G.f.: A(x) = 1/B(-x) where B(x) is the g.f. of A144097.
a(n) = (-1)^(n-1) * (1/n) * Sum_{k=0..n} binomial(n,k) * binomial(3*n+k-2,n-1) for n > 0.
a(n) ~ c*(-1)^(n+1)*4^(-n)*27^n*n^(-3/2)*2F1([-n, 3*n-1], [2*n], -1), with c = 1/(3*sqrt(3*Pi)). - Stefano Spezia, Oct 21 2023
PROG
(PARI) a(n) = if(n==0, 1, (-1)^(n-1)*sum(k=0, n, binomial(n, k)*binomial(3*n+k-2, n-1))/n);
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Jul 22 2023
STATUS
approved