E.g.f.: x/[1-tan(x)].

Terms

a(0) =0a(1) =1a(2) =2a(3) =6a(4) =32a(5) =200a(6) =1536a(7) =13664a(8) =139264a(9) =1595520a(10) =20316160a(11) =284534272a(12) =4347396096a(13) =71958415360