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Erdős problem 26

Let A⊂NA\subset\mathbb{N} be infinite. Must there exist some k≥1k\geq 1 such that almost all integers have a divisor of the form a+ka+k for some a∈Aa\in A? The question as posed follows negatively from Davenport–Erdős (1951). The AI result settles Tenenbaum's harder variant, also negatively: there is an infinite AA such that for every k≥1k\geq 1 the set of multiples of A+kA+k has upper density below 0.340.34.

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The source's own material, retained exactly.

11 retained statements36c6d0fef71a

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FormalConjectures/ErdosProblems/

26.lean

Retained formal statement2 of 10

If we allow for ∑a∈A1a<∞\sum_{a\in A} \frac{1}{a} < \infty then Rusza has found a counter-example.

FormalConjectures/ErdosProblems/26.leanErdos26.erdos_26.variants.rusza1 lineExact file
∃ A, StrictMono A ∧ ¬Erdos26.IsThick A ∧ ∀ (k : ℕ), ¬Erdos26.IsBehrend fun x => A x + k
SolvedStatement only, no proof