O.g.f. A(x) satisfies: A(x) = 1/(1 - x * (d/dx x + x^2*A(x)) ).

Terms

a(0) =1a(1) =1a(2) =3a(3) =8a(4) =29a(5) =106a(6) =438a(7) =1869a(8) =8499a(9) =39926a(10) =195332a(11) =983262a(12) =5099640a(13) =27104535a(14) =147565543a(15) =820663322a(16) =4658281691a(17) =26943982072a(18) =158681719362a(19) =950517101448