E.g.f.: x^2/(x+3-2*exp(x)).

Terms

a(0) =0a(1) =0a(2) =2a(3) =6a(4) =48a(5) =400a(6) =4140a(7) =49644a(8) =681296a(9) =10515600a(10) =180349380a(11) =3402380740a(12) =70023004920