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

Terms

a(0) =1a(1) =4a(2) =17a(3) =90a(4) =539a(5) =3451a(6) =23100a(7) =159720a(8) =1131905a(9) =8178326a(10) =60019533a(11) =446166771a(12) =3352530190a(13) =25422458170a(14) =194302002463