Problem:
Determine whether there exists a matrix with the following properties:
- Every cell is filled with an integer from to .
- For every integer (), the th row and the th column together contain every integer from to .
Problem:
Determine whether there exists a matrix with the following properties:
- Every cell is filled with an integer from to .
- For every integer (), the th row and the th column together contain every integer from to .
Solution:
Answer: no. Fix an integer from to . Let us say that an index "hits" a cell containing the number if the cell is in either the th row or the th column. The conditions stipulate that each index hits exactly one instance of , so the total number of hits is . On the other hand, every cell not lying on the main diagonal is hit by exactly two indices (its row number and its column number), while those on the diagonal are hit only once. In particular, to create an odd total number of hits, must appear on the diagonal. This is a contradiction since there are permissible values of and only spots on the diagonal.