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

Terms

a(0) =1a(1) =1a(2) =3a(3) =13a(4) =61a(5) =309a(6) =1651a(7) =9153a(8) =52161a(9) =303681a(10) =1798459a(11) =10800237a(12) =65614237a(13) =402544597a(14) =2490398139a(15) =15519350593a(16) =97326638145a(17) =613786324353