OFFSET
0,2
FORMULA
a(n) = [x^n] 1/((1+x^2) * (1-x)^(3*n)).
a(n) = binomial(4*n-1, n)*hypergeom([1, (1-n)/2, -n/2], [1/2-2*n, 1-2*n], -1). - Stefano Spezia, Apr 07 2024
PROG
(PARI) a(n) = sum(k=0, n\2, (-1)^k*binomial(4*n-2*k-1, n-2*k));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 06 2024
STATUS
approved