OFFSET
0,4
FORMULA
a(n) = Sum_{k=0..floor(n/2)} (-1)^k * binomial(n,2*k) * binomial(3*k,k)/(2*k+1).
PROG
(PARI) my(N=40, x='x+O('x^N)); Vec(serreverse(x/(x+1/(1+x^2)))/x)
(PARI) a(n) = sum(k=0, n\2, (-1)^k*binomial(n, 2*k)*binomial(3*k, k)/(2*k+1));
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Mar 03 2024
STATUS
approved