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

Terms

a(0) =1a(1) =14a(2) =57a(3) =150a(4) =309a(5) =574a(6) =921a(7) =1444a(8) =2091a(9) =2952a(10) =3919a(11) =5314a(12) =6709a(13) =8534a(14) =10603a(15) =13102a(16) =15593a(17) =18962a(18) =22133a(19) =26332a(20) =30569a(21) =35346a(22) =40097a(23) =46690a(24) =52553a(25) =59394a(26) =66603a(27) =75094a(28) =82833a(29) =93282