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

Terms

a(0) =1a(1) =0a(2) =0a(3) =6a(4) =24a(5) =120a(6) =1440a(7) =15120a(8) =161280a(9) =2177280a(10) =32659200a(11) =518918400a(12) =9101030400a(13) =174356582400