OFFSET
0,5
FORMULA
a(n) = (1/(n+1)) * Sum_{k=0..floor(n/3)} (-1)^k * binomial(n+k,k) * binomial(n-k+1,n-3*k).
PROG
(PARI) a(n) = sum(k=0, n\3, (-1)^k*binomial(n+k, k)*binomial(n-k+1, n-3*k))/(n+1);
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Sep 29 2023
STATUS
approved