OFFSET
0,5
FORMULA
n*a(n) = (2*n-1)*a(n-1) - (n-1)*a(n-2) - (2*n-3)*a(n-3) - 2*(n-2)*a(n-4) - (n-3)*a(n-6).
a(n) = Sum_{k=0..floor(n/3)} (-1)^k * binomial(n-2*k,k)^2.
PROG
(PARI) my(N=40, x='x+O('x^N)); Vec(1/sqrt((1-x+x^3)^2+4*x^4))
(PARI) a(n) = sum(k=0, n\3, (-1)^k*binomial(n-2*k, k)^2);
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Aug 10 2024
STATUS
approved