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

Terms

a(0) =0a(1) =0a(2) =2a(3) =6a(4) =40a(5) =340a(6) =3936a(7) =56714a(8) =976704a(9) =19535688a(10) =444743680a(11) =11349643822a(12) =320813048832