Number of 2 X 2 matrices having all terms in {1,...,n} and determinant = 0 (mod 3).

Terms

a(0) =1a(1) =8a(2) =33a(3) =90a(4) =209a(5) =528a(6) =889a(7) =1432a(8) =2673a(9) =3802a(10) =5297a(11) =8448a(12) =11025a(13) =14216a(14) =20625a(15) =25546a(16) =31393a(17) =42768a(18) =51145a(19) =60824a(20) =79233a(21) =92394a(22) =107297a(23) =135168a(24) =154657a(25) =176392a(26) =216513a(27) =244090a(28) =274481a(29) =330000