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

Terms

a(0) =0a(1) =1a(2) =2a(3) =8a(4) =56a(5) =536a(6) =6528a(7) =96592a(8) =1683072a(9) =33760576a(10) =766283264a(11) =19417068032a(12) =543351873536