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ISL 2022 N6

    Let QQ be a set of prime numbers, not necessarily finite. For a positive integer nn consider its prime factorisation; define p(n)p(n) to be the sum of all the exponents and q(n)q(n) to be the sum of the exponents corresponding only to primes in QQ. A positive integer nn is called special if p(n)+p(n+1)p(n)+p(n+1) and q(n)+q(n+1)q(n)+q(n+1) are both even integers. Prove that there is a constant c>0c>0 independent of the set QQ such that for any positive integer N>100N>100, the number of special integers in [1,N][1, N] is at least cNc N. (For example, if Q={3,7}Q=\{3,7\}, then p(42)=3,q(42)=2,p(63)=3,q(63)=3,p(2022)=3p(42)=3, q(42)=2, p(63)=3, q(63)=3, p(2022)=3, q(2022)=1q(2022)=1. (Costa Rica)

    Dataset text NuminaMath olympiads. Quoted with source.

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