Number of elements (a b, c d) in GL(2,Z) with det = -1, trace n and 0 <= a <= {b, c} <= d.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =1a(5) =4a(6) =1a(7) =4a(8) =4a(9) =4a(10) =2a(11) =10a(12) =1a(13) =5a(14) =7a(15) =12a(16) =1a(17) =10a(18) =4a(19) =10a(20) =12a(21) =4a(22) =6a(23) =24a(24) =4a(25) =12a(26) =7a(27) =10a(28) =5a(29) =26