Number of 2 X 2 matrices having all terms in {1,...,n} and determinant d satisfying -n < d < n.

Terms

a(0) =1a(1) =10a(2) =43a(3) =118a(4) =263a(5) =474a(6) =831a(7) =1258a(8) =1893a(9) =2652a(10) =3685a(11) =4748a(12) =6375a(13) =7918a(14) =9931a(15) =12216a(16) =15015a(17) =17654a(18) =21395a(19) =24726a(20) =29253a(21) =33822a(22) =39011a(23) =43906a(24) =50995a(25) =57210a(26) =64431a(27) =71968a(28) =81075a(29) =88962