E.g.f. cos(x)/(cos(x) - sin(x)).

Terms

a(0) =1a(1) =1a(2) =2a(3) =8a(4) =40a(5) =256a(6) =1952a(7) =17408a(8) =177280a(9) =2031616a(10) =25866752a(11) =362283008a(12) =5535262720a(13) =91620376576