Number of (w,x,y,z) with all terms in {1,...,n} and w+x+y=|x-y|+|y-z|.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =5a(5) =14a(6) =28a(7) =53a(8) =87a(9) =130a(10) =191a(11) =265a(12) =353a(13) =465a(14) =595a(15) =743a(16) =922a(17) =1123a(18) =1347a(19) =1608a(20) =1896a(21) =2211a(22) =2570a(23) =2960a(24) =3382a(25) =3854a(26) =4362a(27) =4906a(28) =5507a(29) =6148