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

Terms

a(0) =2a(1) =1a(2) =4a(3) =6a(4) =48a(5) =120a(6) =1440a(7) =5040a(8) =80640a(9) =362880a(10) =7257600a(11) =39916800a(12) =958003200a(13) =6227020800a(14) =174356582400