G.f. satisfies: A(x) = 1 + 4*x*AGM(1, A(x)^2).

Terms

a(0) =1a(1) =4a(2) =16a(3) =80a(4) =448a(5) =2672a(6) =16640a(7) =106944a(8) =704000a(9) =4722608a(10) =32166784a(11) =221865280a(12) =1546491904a(13) =10876777024a(14) =77091573760a(15) =550088739584