OFFSET
0,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..1000
FORMULA
G.f.: 1 / sqrt(1-4*x/(1+x^4)).
n*a(n) = 2*(2*n-1)*a(n-1) - 2*(n-4)*a(n-4) + 2*(2*n-13)*a(n-5) - (n-8)*a(n-8).
PROG
(PARI) a(n) = sum(k=0, n\4, (-1)^k*binomial(n-1-3*k, k)*binomial(2*n-8*k, n-4*k));
(PARI) my(N=30, x='x+O('x^N)); Vec(1/sqrt(1-4*x/(1+x^4)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Feb 01 2023
STATUS
approved