E.g.f.: Expansion of exp(tanh(tanh(x))).

Terms

a(0) =1a(1) =1a(2) =1a(3) =-3a(4) =-15a(5) =33a(6) =513a(7) =-403a(8) =-31007a(9) =-41247a(10) =2881089a(11) =12404989a(12) =-376412847a(13) =-3175861439a(14) =64825974593a(15) =925805229229