Generalized Catalan numbers C(-2; n).

Terms

a(0) =1a(1) =1a(2) =-1a(3) =5a(4) =-25a(5) =141a(6) =-849a(7) =5349a(8) =-34825a(9) =232445a(10) =-1582081a(11) =10938709a(12) =-76616249a(13) =542472685a(14) =-3876400305a(15) =27919883205a(16) =-202480492905