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Extremal problems for GCDs
Published online by Cambridge University Press: 08 April 2021
Abstract
We prove that if $A \subseteq [X,\,2X]$ and $B \subseteq [Y,\,2Y]$ are sets of integers such that gcd (a, b) ⩾ D for at least δ|A||B| pairs (a, b) ε A × B then $|A||B|{ \ll _{\rm{\varepsilon }}}{\delta ^{ - 2 - \varepsilon }}XY/{D^2}$ . This is a new result even when δ = 1. The proof uses ideas of Koukoulopoulos and Maynard and some additional combinatorial arguments.
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- This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
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- © The Author(s), 2021. Published by Cambridge University Press
Footnotes
The first-named author is supported by a Simons Investigator Award and is grateful to the Simons Foundation for their support. The second-named author is supported by a Postdoctoral Fellowship with the Centre de Recherches Mathématiques and by a Junior Research Fellowship from Trinity College Cambridge.
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