Problem:
Determine all pairs of natural numbers that are solutions of the equation
Problem:
Determine all pairs of natural numbers that are solutions of the equation
Solution:
By checking, we find that for the only solution is the pair . Let us prove that for there are no solutions.
The number must be odd, so . Now from it follows that . Moreover, since (if then ), it must be that , so is an even number.
Adding the number 2 to both sides of the equality gives
Since is even, is a perfect square, so the number is a quadratic residue modulo every odd prime divisor of the number . Therefore
from which it follows that is of the form or . Being a product of such prime numbers, the number itself must also be of that form. However, since , we have , which is a contradiction.
Therefore, the only solution of the given equation is .