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

Terms

a(0) =1a(1) =1a(2) =3a(3) =13a(4) =59a(5) =294a(6) =1549a(7) =8477a(8) =47715a(9) =274468a(10) =1606284a(11) =9533595a(12) =57247969a(13) =347169053a(14) =2123148153a(15) =13079296531a(16) =81087402683a(17) =505543820304