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

Terms

a(0) =1a(1) =0a(2) =2a(3) =6a(4) =48a(5) =360a(6) =3600a(7) =40320a(8) =524160a(9) =7620480a(10) =123379200a(11) =2195424000a(12) =42631142400a(13) =896690995200