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

Terms

a(0) =0a(1) =0a(2) =2a(3) =8a(4) =26a(5) =50a(6) =100a(7) =154a(8) =252a(9) =348a(10) =510a(11) =660a(12) =902a(13) =1118a(14) =1456a(15) =1750a(16) =2200a(17) =2584a(18) =3162a(19) =3648a(20) =4370a(21) =4970a(22) =5852a(23) =6578a(24) =7636a(25) =8500a(26) =9750a(27) =10764a(28) =12222a(29) =13398