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Existence of a rational arithmetic sequence

Source: APMO 2009 Q.4

March 13, 2009
arithmetic sequencenumber theoryrelatively primenumber theory unsolvedHi

Problem Statement

Prove that for any positive integer k k, there exists an arithmetic sequence a1b1,a2b2,a3b3,...,akbk \frac{a_1}{b_1}, \frac{a_2}{b_2}, \frac{a_3}{b_3}, ... ,\frac{a_k}{b_k} of rational numbers, where ai,bi a_i, b_i are relatively prime positive integers for each i \equal{} 1,2,...,k such that the positive integers a1,b1,a2,b2,...,ak,bk a_1, b_1, a_2, b_2, ..., a_k, b_k are all distinct.