E.g.f.: 1/(cos(x) - x*cosh(x)).

Terms

a(0) =1a(1) =1a(2) =3a(3) =15a(4) =89a(5) =685a(6) =6331a(7) =67851a(8) =833265a(9) =11509209a(10) =176580211a(11) =2980609863a(12) =54883547465