E.g.f. tan(x/(1-x)).

Terms

a(0) =0a(1) =1a(2) =2a(3) =8a(4) =48a(5) =376a(6) =3600a(7) =40592a(8) =525952a(9) =7692928a(10) =125303040a(11) =2248366592a(12) =44055035904a(13) =935800603648