OFFSET
0,2
FORMULA
a(n) = Sum_{k=0..n} (-1)^(n-k) * binomial(2*k,k) * binomial(4*k,n-k).
n*a(n) = 2 * ( (2*n-1)*a(n-1) - 4*(2*n-2)*a(n-2) + 6*(2*n-3)*a(n-3) - 4*(2*n-4)*a(n-4) + (2*n-5)*a(n-5) ) for n > 4.
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(1/sqrt(1-4*x*(1-x)^4))
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Mar 25 2023
STATUS
approved