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

Terms

a(0) =1a(1) =4a(2) =17a(3) =32a(4) =71a(5) =104a(6) =187a(7) =247a(8) =380a(9) =484a(10) =685a(11) =823a(12) =1122a(13) =1311a(14) =1690a(15) =1963a(16) =2452a(17) =2767a(18) =3416a(19) =3806a(20) =4557a(21) =5079a(22) =5982a(23) =6546a(24) =7679a(25) =8342a(26) =9591a(27) =10442a(28) =11885a(29) =12770