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

Terms

a(0) =1a(1) =13a(2) =56a(3) =160a(4) =369a(5) =733a(6) =1328a(7) =2216a(8) =3505a(9) =5285a(10) =7680a(11) =10792a(12) =14809a(13) =19813a(14) =26024a(15) =33600a(16) =42721a(17) =53549a(18) =66384a(19) =81336a(20) =98761a(21) =118821a(22) =141784a(23) =167888a(24) =197561a(25) =230917a(26) =268352a(27) =310176a(28) =356753a(29) =408285