E.g.f.: exp(exp(2*(exp(x) - 1)) - 1).

Terms

a(0) =1a(1) =2a(2) =10a(3) =66a(4) =538a(5) =5186a(6) =57402a(7) =714594a(8) =9853978a(9) =148774914a(10) =2436823034a(11) =42979319202a(12) =811254807770