E.g.f.: -log( sqrt(1-x^2) - x ).

Terms

a(0) =1a(1) =2a(2) =5a(3) =24a(4) =129a(5) =960a(6) =7965a(7) =80640a(8) =903105a(9) =11612160a(10) =163451925a(11) =2554675200a(12) =43259364225a(13) =797058662400