Expansion of e.g.f.: 1/(cos(x) - x).

Terms

a(0) =1a(1) =1a(2) =3a(3) =12a(4) =65a(5) =440a(6) =3571a(7) =33824a(8) =366113a(9) =4458240a(10) =60321091a(11) =897774592a(12) =14576528801a(13) =256391130112