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

Terms

a(0) =1a(1) =1a(2) =13a(3) =32a(4) =56a(5) =80a(6) =177a(7) =213a(8) =297a(9) =472a(10) =580a(11) =688a(12) =1037a(13) =1169a(14) =1385a(15) =1872a(16) =2124a(17) =2376a(18) =3133a(19) =3421a(20) =3829a(21) =4784a(22) =5240a(23) =5696a(24) =7017a(25) =7521a(26) =8181a(27) =9760a(28) =10480a(29) =11200