a(n) = n! * [x^n] exp(n*x)/cosh(x).

Terms

a(0) =1a(1) =1a(2) =3a(3) =18a(4) =165a(5) =2000a(6) =29855a(7) =527632a(8) =10762857a(9) =248811264a(10) =6428081979a(11) =183537694208