E.g.f.: -exp(-x/(1-2*x))/(1-2*x).

Terms

a(0) =-1a(1) =-1a(2) =-1a(3) =7a(4) =127a(5) =1711a(6) =23231a(7) =334391a(8) =5144063a(9) =84149983a(10) =1446872959a(11) =25661798119a(12) =454494403199