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Erdős problem 299

Is there an infinite sequence a1<a2<…a_1 < a_2 < \dots such that ai+1−ai=O(1)a_{i+1} - a_i = O(1) and no finite sum of 1ai\frac{1}{a_i} is equal to 1?

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FormalConjectures/ErdosProblems/

299.lean

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The corresponding question is also false if one replaces sequences such that ai+1−ai=O(1)a_{i+1} - a_i = O(1) with sets of positive density, as follows from [Bl21].

The statement is as follows: If A⊂NA \subset \mathbb{N} has positive upper density (and hence certainly if AA has positive density) then there is a finite S⊂AS \subset A such that ∑n∈S1n=1\sum_{n \in S} \frac{1}{n} = 1.

FormalConjectures/ErdosProblems/299.leanErdos299.erdos_299.variants.density1 lineExact file
∀ (A : Set ℕ), 0 ∉ A → 0 < A.upperDensity → ∃ S, ↑S ⊆ A ∧ ∑ n ∈ S, 1 / ↑n = 1
SolvedStatement only, no proof