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

Terms

a(0) =1a(1) =1a(2) =13a(3) =25a(4) =441a(5) =1261a(6) =30213a(7) =115025a(8) =3529201a(9) =16792021a(10) =629401213a(11) =3593565625a(12) =159175688361