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XV Junior Macedonian Mathematical Olympiad

North Macedonia number theory

Problem

Find all integers for which is divisible by .
Solution
From it follows that is a divisor of . Obviously, one solution is .

Let . Then . From it follows that or . The case is not possible (). From it follows that i.e. . The last inequality is satisfied for . Checking each value, we conclude that and satisfy the initial condition.

Finally .
Final answer
{-5, 0, 1}

Techniques

Divisibility / FactorizationPolynomial operationsLinear and quadratic inequalities