Number of 2 X 2 singular integer matrices with entries from {2,...,n}.

Terms

a(0) =0a(1) =1a(2) =6a(3) =15a(4) =28a(5) =53a(6) =74a(7) =111a(8) =152a(9) =209a(10) =246a(11) =339a(12) =384a(13) =473a(14) =582a(15) =695a(16) =756a(17) =917a(18) =986a(19) =1175a(20) =1340a(21) =1493a(22) =1578a(23) =1855a(24) =2008a(25) =2193a(26) =2398a(27) =2683a(28) =2792a(29) =3185