Generalized Catalan numbers C(-1; n).

Terms

a(0) =1a(1) =1a(2) =0a(3) =1a(4) =-2a(5) =6a(6) =-18a(7) =57a(8) =-186a(9) =622a(10) =-2120a(11) =7338a(12) =-25724a(13) =91144a(14) =-325878a(15) =1174281a(16) =-4260282a(17) =15548694a(18) =-57048048a(19) =210295326a(20) =-778483932a(21) =2892818244a(22) =-10786724388a(23) =40347919626a(24) =-151355847012a(25) =569274150156