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

Terms

a(0) =1a(1) =8a(2) =28a(3) =96a(4) =193a(5) =448a(6) =728a(7) =1360a(8) =1985a(9) =3264a(10) =4420a(11) =6696a(12) =8641a(13) =12296a(14) =15360a(15) =20896a(16) =25361a(17) =33344a(18) =39636a(19) =50680a(20) =59289a(21) =74056a(22) =85376a(23) =104728a(24) =119377a(25) =144032a(26) =162588a(27) =193568a(28) =216585a(29) =254880