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SELECTION and TRAINING SESSION

Belarus number theory

Problem

Given such that and the numbers are composite. Prove that there exist distinct primes such that is divisible by for any .
Solution
We call the number from the problem condition convenient if it has at least distinct prime divisors, otherwise we call the number inconvenient. It is easy to see that we may consider inconvenient numbers only. Take one of them, , where all are primes, . Since there exists an with , so we can choose . In a similar way we can choose prime divisors for other inconvenient numbers. It remains to note that for different inconvenient numbers the chosen prime divisors are different.

Techniques

Prime numbersFactorization techniques