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Positive Lower Density for Hofstadter's ab-1 Problem

Samuel Korsky

math.NTarXiv:2608.07910

Abstract

Let A be the smallest set of positive integers containing 2 and 3 such that ab-1∈ A whenever a,b∈ A are distinct. We prove that A has positive lower density, answering a problem of Erdős attributed to Hofstadter.

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