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

Terms

a(0) =1a(1) =2a(2) =6a(3) =26a(4) =148a(5) =1032a(6) =8464a(7) =79592a(8) =842832a(9) =9914336a(10) =128162464a(11) =1804852128a(12) =27489582784a(13) =450089665664