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

Terms

a(0) =1a(1) =1a(2) =2a(3) =9a(4) =40a(5) =202a(6) =1068a(7) =5884a(8) =33356a(9) =193365a(10) =1140940a(11) =6829601a(12) =41372238a(13) =253156085a(14) =1562416632a(15) =9714660195a(16) =60795387840a(17) =382639224327