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) =2a(3) =4a(4) =3a(5) =7a(6) =4a(7) =8a(8) =6a(9) =12a(10) =5a(11) =14a(12) =7a(13) =13a(14) =13a(15) =20a(16) =5a(17) =20a(18) =10a(19) =24a(20) =14a(21) =22a(22) =12a(23) =28a(24) =18a(25) =30a(26) =14a(27) =22a(28) =17a(29) =48