2006 IMO Problems/Problem 4
Problem
Determine all pairs of integers such that
Solution
: LHS integer iff , but then . is a solution. for no solution. so assume . LHS is odd, so writing gives us . are coprime, and so are . so or vice versa, but both lead to a contradiction
NOTE: This solution does not seem to be correct. Take e.g. . Then and . The argument of the solution is promising, but the following is not true: Let , be co-prime and let , be also coprime and additionally let . Then it must either be or .