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

Terms

a(0) =0a(1) =2a(2) =2a(3) =12a(4) =24a(5) =240a(6) =720a(7) =10080a(8) =40320a(9) =725760a(10) =3628800a(11) =79833600a(12) =479001600a(13) =12454041600a(14) =87178291200