Number of (w,x,y,z) with all terms in {0,...,n} and even range.

Terms

a(0) =1a(1) =2a(2) =53a(3) =104a(4) =349a(5) =594a(6) =1273a(7) =1952a(8) =3401a(9) =4850a(10) =7501a(11) =10152a(12) =14533a(13) =18914a(14) =25649a(15) =32384a(16) =42193a(17) =52002a(18) =65701a(19) =79400a(20) =97901a(21) =116402a(22) =140713a(23) =165024a(24) =196249a(25) =227474a(26) =266813a(27) =306152a(28) =354901a(29) =403650