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

Terms

a(0) =1a(1) =1a(2) =3a(3) =12a(4) =53a(5) =261a(6) =1356a(7) =7315a(8) =40563a(9) =229791a(10) =1324163a(11) =7737387a(12) =45737670a(13) =273023637a(14) =1643468253a(15) =9964808217a(16) =60803287261a(17) =373086879114