MathDB
Argentina Cono Sur TST 2013. Problem 6

Source:

January 3, 2015

Problem Statement

Let m4m\geq 4 and n4n\geq 4. An integer is written on each cell of a m×nm \times n board. If each cell has a number equal to the arithmetic mean of some pair of numbers written on its neighbouring cells, determine the maximum amount of distinct numbers that the board may have.
Note: two neighbouring cells share a common side.