OFFSET
0,3
FORMULA
a(n) = (-1)^n * Sum_{k=0..n} 4^k * binomial((n-k)/2,k).
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(1/(1+x*sqrt(1-4*x)))
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Seiichi Manyama, Apr 09 2023
STATUS
approved