Number of operations not greater than (2n/k)².
Source: Baltic Way 2005/6
November 7, 2005
combinatorics proposedcombinatorics
Problem Statement
Let and be positive integers satisfying . A deck of different playing cards is shuffled by repeating the operation of reversing the order of topmost cards and moving these to the bottom of the deck. Prove that the deck will be back in its initial order after a number of operations not greater than .