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

Terms

a(0) =1a(1) =1a(2) =3a(3) =12a(4) =52a(5) =255a(6) =1320a(7) =7095a(8) =39213a(9) =221403a(10) =1271552a(11) =7404933a(12) =43624359a(13) =259524942a(14) =1556899818a(15) =9407758965a(16) =57208440741a(17) =349830089730