Number of 2 X 2 matrices with entries mod n and nonzero determinant.

Terms

a(0) =0a(1) =6a(2) =48a(3) =168a(4) =480a(5) =966a(6) =2016a(7) =3360a(8) =5616a(9) =8550a(10) =13200a(11) =17832a(12) =26208a(13) =34566a(14) =45840a(15) =59520a(16) =78336a(17) =95526a(18) =123120a(19) =147240a(20) =181776a(21) =219846a(22) =267168a(23) =307488a(24) =372000a(25) =433446a(26) =505440a(27) =580776a(28) =682080a(29) =762150