Expansion of e.g.f. 1/(1-x-2*x^3).

Terms

a(0) =1a(1) =1a(2) =2a(3) =18a(4) =120a(5) =840a(6) =9360a(7) =115920a(8) =1491840a(9) =22861440a(10) =395539200a(11) =7304774400a(12) =148011494400