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55rd Ukrainian National Mathematical Olympiad - Fourth Round

Ukraine number theory

Problem

Find all integer , such that:
Solution
If integer number satisfies the given condition, then can be presented as product of four pairwise distinct integers. Since the integer divisors of this number are only , and , we have that sought-for divisors are and . Indeed, if the absolute value of one of divisors is equal to then others are not less than by absolute value, a contradiction. Since is the biggest factor, it should be equal to . Also we see that satisfies the condition of the problem.
Final answer
2015

Techniques

Techniques: modulo, size analysis, order analysis, inequalitiesPolynomial operations