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

Terms

a(0) =1a(1) =1a(2) =3a(3) =12a(4) =54a(5) =267a(6) =1392a(7) =7532a(8) =41901a(9) =238143a(10) =1376781a(11) =8071266a(12) =47868441a(13) =286685994a(14) =1731414114a(15) =10532802108a(16) =64482068433a(17) =396972197892