Number of 2 X 2 matrices with all elements in {0,1,...,n} and nonnegative even determinant.

Terms

a(0) =1a(1) =10a(2) =48a(3) =112a(4) =285a(5) =490a(6) =968a(7) =1448a(8) =2465a(9) =3410a(10) =5280a(11) =6904a(12) =10021a(13) =12610a(14) =17400a(15) =21312a(16) =28321a(17) =33866a(18) =43704a(19) =51336a(20) =64661a(21) =74898a(22) =92416a(23) =105680a(24) =128297a(25) =145234a(26) =173712a(27) =194928a(28) =230333a(29) =256410