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

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =22a(5) =76a(6) =290a(7) =1225a(8) =5616a(9) =27758a(10) =147050a(11) =829926a(12) =4966258a(13) =31382572a(14) =208676004a(15) =1455540594a(16) =10620614461a(17) =80869622604a(18) =641177678068