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

Terms

a(0) =1a(1) =2a(2) =4a(3) =18a(4) =72a(5) =480a(6) =2880a(7) =25200a(8) =201600a(9) =2177280a(10) =21772800a(11) =279417600a(12) =3353011200a(13) =49816166400a(14) =697426329600