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

Terms

a(0) =0a(1) =0a(2) =1a(3) =7a(4) =21a(5) =46a(6) =86a(7) =144a(8) =223a(9) =327a(10) =459a(11) =622a(12) =820a(13) =1056a(14) =1333a(15) =1655a(16) =2025a(17) =2446a(18) =2922a(19) =3456a(20) =4051a(21) =4711a(22) =5439a(23) =6238a(24) =7112a(25) =8064a(26) =9097a(27) =10215a(28) =11421a(29) =12718