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

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =16a(5) =48a(6) =152a(7) =500a(8) =1688a(9) =5816a(10) =20368a(11) =72288a(12) =259424a(13) =939808a(14) =3432192a(15) =12622416a(16) =46706144a(17) =173762016a(18) =649569216a(19) =2438748864a(20) =9191656192a(21) =34765298944a(22) =131912452864a(23) =501987944832