Number of 2 X 2 matrices having all terms in {1,...,n} and determinant = 1 (mod 3).

Terms

a(0) =0a(1) =4a(2) =24a(3) =83a(4) =208a(5) =384a(6) =756a(7) =1332a(8) =1944a(9) =3099a(10) =4672a(11) =6144a(12) =8768a(13) =12100a(14) =15000a(15) =19995a(16) =26064a(17) =31104a(18) =39588a(19) =49588a(20) =57624a(21) =70931a(22) =86272a(23) =98304a(24) =117984a(25) =140292a(26) =157464a(27) =185283a(28) =216400a(29) =240000