OFFSET
0,5
FORMULA
G.f.: 1 / sqrt(1+4*x^4/(1-x)).
n*a(n) = 2*(n-1)*a(n-1) - (n-2)*a(n-2) - 2*(2*n-4)*a(n-4) + 2*(2*n-7)*a(n-5).
PROG
(PARI) a(n) = sum(k=0, n\4, (-1)^k*binomial(n-1-3*k, n-4*k)*binomial(2*k, k));
(PARI) my(N=40, x='x+O('x^N)); Vec(1/sqrt(1+4*x^4/(1-x)))
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Feb 03 2023
STATUS
approved