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

Terms

a(0) =0a(1) =0a(2) =1a(3) =9a(4) =23a(5) =52a(6) =92a(7) =155a(8) =234a(9) =344a(10) =475a(11) =645a(12) =841a(13) =1084a(14) =1358a(15) =1687a(16) =2052a(17) =2480a(18) =2949a(19) =3489a(20) =4075a(21) =4740a(22) =5456a(23) =6259a(24) =7118a(25) =8072a(26) =9087a(27) =10205a(28) =11389a(29) =12684