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Estonian Mathematical Olympiad

Estonia number theory

Problem

Does there exist a positive integer such that
Solution
Answer: No.

The numbers , , and give remainders , , and , respectively, when divided by . Raising to powers results in remainders , and raising to the same powers results in remainders . Thus, the remainders of the left side of the given equation for powers are . The remainder of the right side is for every . The contradiction shows that there is no positive integer that satisfies the given equation.

Clearly is not suitable, because . It is also easy to verify that



For , there are no integer solutions to the equation by Fermat's Last Theorem.
Final answer
No

Techniques

Modular ArithmeticMultiplicative orderTechniques: modulo, size analysis, order analysis, inequalities