E.g.f. exp(tan(x)+tan(x)^2+tan(x)^3).

Terms

a(0) =1a(1) =1a(2) =3a(3) =15a(4) =73a(5) =537a(6) =3899a(7) =35623a(8) =345553a(9) =3767185a(10) =44993331a(11) =575013087a(12) =8040614041a(13) =118459611753