English

A note on the Diophantine equation $2ln^{2} = 1+q+ \cdots +q^{\alpha}$ and application to odd perfect numbers

Number Theory 2023-12-01 v3

Abstract

Let NN be an odd perfect number. Then, Euler proved that there exist some integers n,αn, \alpha and a prime qq such that N=n2qαN = n^{2}q^{\alpha}, qnq \nmid n, and qα1mod4q \equiv \alpha \equiv 1 \bmod 4. In this note, we prove that the ratio σ(n2)qα\frac{\sigma(n^{2})}{q^{\alpha}} is neither a square nor a square times a single prime unless α=1\alpha = 1. It is a direct consequence of a certain property of the Diophantine equation 2ln2=1+q++qα2ln^{2} = 1+q+ \cdots +q^{\alpha}, where ll denotes one or a prime, whose proof is based on the prime ideal factorization in the quadratic orders Z[1q]\mathbb{Z}[\sqrt{1-q}] and the primitive solutions of generalized Fermat equations xβ+yβ=2z2x^{\beta}+y^{\beta} = 2z^{2}. We give also a slight generalization to odd multiply perfect numbers.

Keywords

Cite

@article{arxiv.2309.17084,
  title  = {A note on the Diophantine equation $2ln^{2} = 1+q+ \cdots +q^{\alpha}$ and application to odd perfect numbers},
  author = {Yoshinosuke Hirakawa},
  journal= {arXiv preprint arXiv:2309.17084},
  year   = {2023}
}

Comments

6 pages. Comments welcome!