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

Terms

a(0) =1a(1) =2a(2) =8a(3) =54a(4) =480a(5) =5280a(6) =69840a(7) =1078560a(8) =19031040a(9) =377758080a(10) =8331724800a(11) =202138675200