Combinatorics in a cube
Source: Baltic Way 2016, Problem 14
November 5, 2016
combinatorics
Problem Statement
A cube consists of unit cubes each containing an integer. At each move, you choose a unit cube and increase by all the integers in the neighbouring cubes having a face in common with the chosen cube. Is it possible to reach a position where all the integers are divisible by no matter what the starting position is?