Number of 2 X 2 singular integer matrices with elements from {1,...,n}.

Terms

a(0) =0a(1) =1a(2) =6a(3) =15a(4) =32a(5) =49a(6) =86a(7) =111a(8) =160a(9) =209a(10) =278a(11) =319a(12) =432a(13) =481a(14) =582a(15) =703a(16) =832a(17) =897a(18) =1078a(19) =1151a(20) =1360a(21) =1537a(22) =1702a(23) =1791a(24) =2096a(25) =2257a(26) =2454a(27) =2671a(28) =2976a(29) =3089