OFFSET
0,2
COMMENTS
Diagonal of rational function 1/(1 - (x + y + x^3*y^2)). - Seiichi Manyama, Mar 23 2023
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..1000
FORMULA
G.f.: 1/sqrt(1 - 4*x*(1 + x^2)).
n*a(n) = 2*(2*n-1)*a(n-1) + 2*(2*n-3)*a(n-3).
PROG
(PARI) a(n) = sum(k=0, n\3, binomial(n-2*k, k)*binomial(2*(n-2*k), n-2*k));
(PARI) my(N=30, x='x+O('x^N)); Vec(1/sqrt(1-4*x*(1+x^2)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jan 31 2023
STATUS
approved