For what values of does there exist an array of entries -1, 0 or 1 such that the sums obtained by summing the elements of the rows and the columns are all different?
%V0
For what values of $n$ does there exist an $n \times n$ array of entries -1, 0 or 1 such that the $2 \cdot n$ sums obtained by summing the elements of the rows and the columns are all different?
Izvor: Međunarodna matematička olimpijada, shortlist 1988
Školjka 
does there exist an 
array of entries -1, 0 or 1 such that the 
sums obtained by summing the elements of the rows and the columns are all different?