Expansion of e.g.f. 3*x/(1 - 2*x).

Terms

a(0) =0a(1) =3a(2) =12a(3) =72a(4) =576a(5) =5760a(6) =69120a(7) =967680a(8) =15482880a(9) =278691840a(10) =5573836800a(11) =122624409600