OFFSET
0,3
FORMULA
G.f.: 1 / (1 - Sum(k>=1} (2*k)!/2 * x^k)).
a(0) = 1; a(n) = Sum_{k=1..n} (2*k)!/2 * a(n-k).
PROG
(PARI) my(N=20, x='x+O('x^N)); Vec(1/(1-sum(k=1, N, (2*k)!/2*x^k)))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Feb 17 2024
STATUS
approved