1 through 50 on blackboard; replace any two with difference
Source: Kyrgyzstan 2012, Problem 6
May 2, 2013
invariantmodular arithmeticinductionalgorithmcombinatorics unsolvedcombinatorics
Problem Statement
The numbers are written on a blackboard. Each minute any two numbers are erased and their positive difference is written instead. At the end one number remains. Which values can take this number?