The EGPS conjecture on preimages of density-zero sets under the proper-divisor sum

From papers

Let s(n)=dn, d<nds(n)=\sum_{d\mid n,\ d<n}d be the sum-of-proper-divisors function, and let A\mathcal{A} be a set of integers with asymptotic density zero, meaning that

limx1x#{nx:nA}=0.\lim_{x\to\infty}\frac{1}{x}\#\{n\leq x:n\in\mathcal{A}\}=0.

EGPS conjecture. The preimage s1(A)s^{-1}(\mathcal{A}) also has asymptotic density zero.

The conjecture concerns whether the proper-divisor sum can produce a positive-density set of inputs from a density-zero target set. The full EGPS conjecture is still open today.

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Sources & referencesView supporting material

Primary source

Kübra Benli, Giulia Cesana, Cécile Dartyge, Charlotte Dombrowsky and Lola Thompson, “Sums of proper divisors with missing digits”, arXiv:2307.12859 (2023).

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