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

Terms

a(0) =0a(1) =0a(2) =2a(3) =6a(4) =48a(5) =480a(6) =5760a(7) =80640a(8) =1290240a(9) =23224320a(10) =464486400a(11) =10218700800a(12) =245248819200