E.g.f.: tan(x)/(1+LambertW(-x)).

Terms

a(0) =0a(1) =1a(2) =2a(3) =14a(4) =116a(5) =1376a(6) =19926a(7) =346128a(8) =6964712a(9) =159396352a(10) =4085415850a(11) =115906440704