214292575376domain: NAppears in sequencesG.f. A(x) = Product_{n>=1} P(n,x), 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=21A351512