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

Terms

a(0) =0a(1) =2a(2) =13a(3) =64a(4) =144a(5) =362a(6) =617a(7) =1200a(8) =1776a(9) =2986a(10) =4101a(11) =6264a(12) =8160a(13) =11714a(14) =14657a(15) =20064a(16) =24464a(17) =32266a(18) =38485a(19) =49320a(20) =57752a(21) =72354a(22) =83585a(23) =102632a(24) =117120a(25) =141578a(26) =159917a(27) =190592a(28) =213496a(29) =251370