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arXiv · 1812.06566

Primary Pseudoperfect Numbers, Arithmetic Progressions, and the Erd\H{o}s-Moser Equation

Jonathan Sondow·Kieren MacMillan
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Abstract

A primary pseudoperfect number (PPN) is an integer $K > 1$ such that the reciprocals of $K$ and its prime factors sum to 1. PPNs arise in studying perfectly weighted graphs and singularities of algebraic surfaces, and are related to Sylvester's sequence, Giuga numbers, Zn\'am's problem, the inheritance problem, and Curtiss's bound on solutions of a unit fraction equation. Here we show $K \equiv 6 \pmod{6^2}$ if $6\mid K$, and uncover a remarkable $7$-term arithmetic progression of residues modulo $6^2\cdot8$ in the sequence of known PPNs. On that basis, we pose a conjecture which leads to a conditional proof of the new record lower bound $k>10^{3.99\times10^{20}}$ on any non-trivial solution to the Erd\H{o}s-Moser Diophantine equation $1^n + 2^n + \dotsb + k^n = (k+1)^n$.

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Jonathan Sondow, Kieren MacMillan. 2018-12-17. Primary Pseudoperfect Numbers, Arithmetic Progressions, and the Erd\H{o}s-Moser Equation. https://doi.org/10.4169/amer.math.monthly.124.3.232

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