OFFSET
0,4
FORMULA
a(n) = Sum_{k=0..floor(n/3)} binomial(2*k,k) * binomial(n-k-1,n-3*k).
PROG
(PARI) my(N=40, x='x+O('x^N)); Vec(1/sqrt(1-4*x^3/(1-x)^2))
(PARI) a(n) = sum(k=0, n\3, binomial(2*k, k) * binomial(n-k-1, n-3*k));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Oct 04 2024
STATUS
approved