MathDB
Moving pairs of knights

Source: Mexico National Olympiad 2017, Problem 1

November 6, 2017
combinatoricsboardknight

Problem Statement

A knight is placed on each square of the first column of a 2017×20172017 \times 2017 board. A move consists in choosing two different knights and moving each of them to a square which is one knight-step away. Find all integers kk with 1k20171 \leq k \leq 2017 such that it is possible for each square in the kk-th column to contain one knight after a finite number of moves.
Note: Two squares are a knight-step away if they are opposite corners of a 2×32 \times 3 or 3×23 \times 2 board.