E.g.f.: exp(1 / (1 - arctan(x)) - 1).

Terms

a(0) =1a(1) =1a(2) =3a(3) =11a(4) =49a(5) =265a(6) =1683a(7) =12035a(8) =95169a(9) =832337a(10) =7998467a(11) =83033403a(12) =922112305a(13) =10978263257a(14) =139956480467