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

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =19a(5) =64a(6) =227a(7) =832a(8) =3126a(9) =11980a(10) =46646a(11) =184003a(12) =733783a(13) =2953434a(14) =11982265a(15) =48949631a(16) =201182110a(17) =831292029a(18) =3451336467a(19) =14390479996a(20) =60232976244a(21) =252992172572