Problem

Source: Serbia NMO 2010 problem 5

Tags: linear algebra, matrix, combinatorics unsolved, combinatorics



An $n\times n$ table whose cells are numerated with numbers $1, 2,\cdots, n^2$ in some order is called Naissus if all products of $n$ numbers written in $n$ scattered cells give the same residue when divided by $n^2+1$. Does there exist a Naissus table for $(a) n = 8;$ $(b) n = 10?$ ($n$ cells are scattered if no two are in the same row or column.) Proposed by Marko Djikic