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

Terms

a(0) =1a(1) =1a(2) =4a(3) =21a(4) =148a(5) =1305a(6) =13806a(7) =170401a(8) =2403640a(9) =38143377a(10) =672552730a(11) =13044463641a(12) =276003553860