51854273344domain: NAppears in sequencesG.f. A(x) = lim_{n->infinity} (1 - P(n,x))/(-2*x)^n, where P(1,x) = 1/sqrt(1 - 4*x), and P(n+1,x) = 1/sqrt(1 - 4*x + 4*x*P(n,x)) for n >= 1.at n=20A351510