G.f. satisfies A(x) = 1 + x*A(x)^2 + x^2*(1-x)*A(x)^3.

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =33a(5) =127a(6) =517a(7) =2173a(8) =9379a(9) =41293a(10) =184765a(11) =837695a(12) =3840089a(13) =17768585a(14) =82879635a(15) =389283441a(16) =1839640281a(17) =8740574143a(18) =41728175821a(19) =200070896725a(20) =962982898195