E.g.f.: -sin(LambertW(-x)).

Terms

a(0) =0a(1) =1a(2) =2a(3) =8a(4) =52a(5) =476a(6) =5646a(7) =82368a(8) =1426888a(9) =28623376a(10) =652516090a(11) =16660233600a(12) =470930272572