Erdős Problem #355 — Lacunary Reciprocal Sums Representing an Interval

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Does there exist a lacunary sequence A=(An)n∈NA=(A_n)_{n\in\mathbb N} of natural numbers and real numbers u<vu<v such that every rational number in the open interval (u,v)(u,v) is a finite subsum of reciprocal terms of AA? More precisely, AA is lacunary if there is some constant λ>1\lambda>1 such that

An+1An≥λ\frac{A_{n+1}}{A_n}\ge\lambda

for all n≥1n\ge1, and the required representation property is

∀q∈Q,u<q<v ⟹ ∃A′⊆A finite such that q=∑a∈A′1a.\forall q\in\mathbb Q,\quad u<q<v\ \Longrightarrow\ \exists A'\subseteq A\text{ finite such that }q=\sum_{a\in A'}\frac1a.
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