Number of 2 X 2 matrices having all terms in {1,...,n} and nonnegative determinant.

Terms

a(0) =1a(1) =11a(2) =48a(3) =144a(4) =337a(5) =691a(6) =1256a(7) =2128a(8) =3385a(9) =5139a(10) =7480a(11) =10584a(12) =14521a(13) =19499a(14) =25664a(15) =33184a(16) =42209a(17) =53027a(18) =65736a(19) =80680a(20) =98009a(21) =117979a(22) =140816a(23) =166936a(24) =196441a(25) =229715a(26) =267056a(27) =308816a(28) =355185a(29) =406755