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

Terms

a(0) =1a(1) =2a(2) =8a(3) =44a(4) =304a(5) =2512a(6) =24064a(7) =261536a(8) =3173888a(9) =42483968a(10) =621159424a(11) =9841950208a(12) =167879268352