E.g.f.: -log(1 + x + log(1 - x)).

Terms

a(0) =0a(1) =1a(2) =2a(3) =9a(4) =44a(5) =280a(6) =2064a(7) =17738a(8) =172528a(9) =1880856a(10) =22686960a(11) =300193872a(12) =4323063744a(13) =67323469200