224166303708domain: NAppears in sequencesG.f. A(x) = lim_{n->infinity} (P(n) - 1)/(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=21A351509