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

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Let s(n)=∑d∣n, 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

lim⁡x→∞1x#{n≤x:n∈A}=0.\lim_{x\to\infty}\frac{1}{x}\#\{n\leq x:n\in\mathcal{A}\}=0.

EGPS conjecture. The preimage s−1(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.

References

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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