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KöMaL problem A, 2020

Number theory Difficulty 6.0 National Olympiad Prove it Hungary

Let k≥t≥2k\ge t\ge 2 positive integers. For integers n≥kn\ge k let pnp_n be the probability that if we choose kk from the first nn positive integers randomly, any tt of the kk chosen integers have greatest common divisor 1. Let qnq_n be the probability that if we choose k−t+1k-t+1 from the first nn positive integers the product is not divisible by a perfect tt-th power that is greater then 1.

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