E.g.f.: -cos(x)*LambertW(-x).

Terms

a(0) =0a(1) =1a(2) =2a(3) =6a(4) =52a(5) =540a(6) =6846a(7) =104832a(8) =1883848a(9) =38889360a(10) =907247770a(11) =23608391840a(12) =678039307452