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

Terms

a(0) =1a(1) =1a(2) =3a(3) =11a(4) =52a(5) =258a(6) =1344a(7) =7260a(8) =40290a(9) =228363a(10) =1316414a(11) =7694154a(12) =45491247a(13) =271594897a(14) =1635068538a(15) =9914851401a(16) =60503259435a(17) =371269891422