Number of (w,x,y,z) with all terms in {0,...,n} and w=max{w,x,y,z}-2*min{w,x,y,z}.

Terms

a(0) =1a(1) =8a(2) =27a(3) =83a(4) =162a(5) =277a(6) =495a(7) =730a(8) =1025a(9) =1513a(10) =1988a(11) =2547a(12) =3413a(13) =4212a(14) =5119a(15) =6471a(16) =7678a(17) =9017a(18) =10963a(19) =12662a(20) =14517a(21) =17165a(22) =19440a(23) =21895a(24) =25353a(25) =28288a(26) =31427a(27) =35803a(28) =39482a(29) =43389