Number of 2 X 2 matrices with all terms in {0,1,...,n} and (sum of terms) = n+2.

Terms

a(0) =0a(1) =4a(2) =19a(3) =40a(4) =68a(5) =104a(6) =149a(7) =204a(8) =270a(9) =348a(10) =439a(11) =544a(12) =664a(13) =800a(14) =953a(15) =1124a(16) =1314a(17) =1524a(18) =1755a(19) =2008a(20) =2284a(21) =2584a(22) =2909a(23) =3260a(24) =3638a(25) =4044a(26) =4479a(27) =4944a(28) =5440a(29) =5968