English

Divisor sums representable as the sum of two squares

Number Theory 2019-03-01 v1

Abstract

Let s(n)s(n) denote the sum of the proper divisors of the natural number nn. We show that the number of nxn \leq x such that s(n)s(n) is a sum of two squares has order of magnitude x/logxx/\sqrt{\log x}, which agrees with the count of nxn \leq x which are a sum of two squares. Our result confirms a special case of a conjecture of Erd{\H o}s, Granville, Pomerance and Spiro, who in a 1990 paper asserted that if AN\mathcal{A} \subset \mathbb{N} has asymptotic density zero (e.g. if A\mathcal{A} is the set of nxn \leq x which are a sum of two squares), then s1(A)s^{-1}(\mathcal{A}) also has asymptotic density zero.

Keywords

Cite

@article{arxiv.1902.11171,
  title  = {Divisor sums representable as the sum of two squares},
  author = {Lee Troupe},
  journal= {arXiv preprint arXiv:1902.11171},
  year   = {2019}
}

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14 pages