OFFSET
0,2
FORMULA
a(n) = [x^n] 1/((1-x+x^3) * (1-x)^n).
a(n) = binomial(2*n, n)*hypergeom([1, (1-n)/3, (2-n)/3, -n/3], [1/2-n, -n, 1+n], 27/4). - Stefano Spezia, Apr 07 2024
PROG
(PARI) a(n) = sum(k=0, n\3, (-1)^k*binomial(2*n-2*k, n-3*k));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 06 2024
STATUS
approved