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

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =17a(5) =52a(6) =167a(7) =558a(8) =1912a(9) =6683a(10) =23736a(11) =85426a(12) =310861a(13) =1141837a(14) =4227938a(15) =15764474a(16) =59140089a(17) =223062670a(18) =845388258a(19) =3217750229a(20) =12295043520a(21) =47144444476a(22) =181349473833a(23) =699629022954