We try to characterize the number of di .erent elements in A = {a 1, a 2 a n}j n such that {a 1 +a 2, a 2 +a 3a n +a 1}=Z n or {a 2 -a 1, a 3 -a 2a 1 -a n}=Z n .Partial results are proved.E.g.,in the second case for odd n all the integers in ((3 n +1)/4, n) occur.