OFFSET
0,4
FORMULA
a(n) = Sum_{k=0..floor(n/2)} (-1)^k * binomial(n+3*k,k) * binomial(n+2*k,n-2*k) / (4*k+1).
PROG
(PARI) a(n) = sum(k=0, n\2, (-1)^k*binomial(n+3*k, k)*binomial(n+2*k, n-2*k)/(4*k+1));
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Nov 02 2023
STATUS
approved