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Number theory Difficulty 4.6 AIME Prove it Belarus

Given m,nNm, n \in \mathbb{N} such that m>nn1m > n^{n-1} and the numbers m+1,m+2,,m+nm+1, m+2, \dots, m+n are composite.
Prove that there exist distinct primes p1,p2,,pnp_1, p_2, \dots, p_n such that m+km+k is divisible by pkp_k for any k=1,2,,nk = 1, 2, \dots, n.

Solution

We call the number m+km + k from the problem condition convenient if it has at least nn distinct prime divisors, otherwise we call the number m+km + k inconvenient. It is easy to see that we may consider inconvenient numbers only. Take one of them, m+k=q1a1q2a2qlalm + k = q_1^{a_1} q_2^{a_2} \dots q_l^{a_l}, where all qiq_i are primes, ln1l \le n - 1. Since
q1a1q2a2qlal=m+k>nn1nl, q_1^{a_1} q_2^{a_2} \dots q_l^{a_l} = m + k > n^{n-1} \ge n^l,
there exists an ii with qiai>nq_i^{a_i} > n, so we can choose pk=qip_k = q_i. 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.

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