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

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =19a(5) =64a(6) =225a(7) =816a(8) =3031a(9) =11473a(10) =44096a(11) =171631a(12) =675130a(13) =2679728a(14) =10719237a(15) =43168826a(16) =174885089a(17) =712222799a(18) =2914150406a(19) =11973792218a(20) =49385167369a(21) =204386777160a(22) =848530495383