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

Terms

a(0) =1a(1) =10a(2) =37a(3) =96a(4) =205a(5) =386a(6) =665a(7) =1072a(8) =1641a(9) =2410a(10) =3421a(11) =4720a(12) =6357a(13) =8386a(14) =10865a(15) =13856a(16) =17425a(17) =21642a(18) =26581a(19) =32320a(20) =38941a(21) =46530a(22) =55177a(23) =64976a(24) =76025a(25) =88426a(26) =102285a(27) =117712a(28) =134821a(29) =153730