Erdős Problem #143 — Let A⊂(1,∞)A\subset (1,\infty) be a countably infinite set such that for all x≠y∈Ax\neq y\in A and integers k≥1k\geq 1 we have ∣kx−y∣≥1.\lvert kx -y\rvert \geq 1. Does this imply that AA is sparse?

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Let A⊂(1,∞)A\subset (1,\infty) be a countably infinite set such that for all x≠y∈Ax\neq y\in A and integers k≥1k\geq 1 we have ∣kx−y∣≥1. \lvert kx -y\rvert \geq 1. Does this imply that AA is sparse? In particular, does this imply that ∑x∈A1xlog⁡x<∞\sum_{x\in A}\frac{1}{x\log x}<\infty or ∑x<nx∈A1x=o(log⁡n)?\sum_{\substack{x <n\\ x\in A}}\frac{1}{x}=o(\log n)?

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