English

A note on necessary conditions for a friend of 10

Number Theory 2025-01-20 v5

Abstract

Solitary numbers are shrouded with mystery. A folklore conjecture assert that 10 is a solitary number i.e. it has no friends. In this article, we establish that if NN is a friend of 1010 then it must be odd square with at least seven distinct prime factors, with 55 being the least one. Moreover there exists a prime factor pp of NN such that 2a+10(modf)2a+1\equiv 0 \pmod f and 5f1(modp)5^{f}\equiv 1 \pmod p where ff is the smallest odd positive integer greater than 11 and less than or equal to min{2a+1,p1}\min\{ 2a+1,p-1\}, provided 52aN5^{2a}\mid \mid N. Further, there exist prime factors pp and qq (not necessarily distinct) of NN such that p1(mod10)p\equiv1 \pmod {10} and q1(mod6)q\equiv 1\pmod 6. Besides, we prove that if a Fermat prime FkF_k divides NN then NN must have a prime factor congruent to 11 modulo 2Fk2F_k. Also, if we consider the form of NN as N=52am2N=5^{2a}m^2 then mm is non square-free. Furthermore, we show that Ω(N)2ω(N)+6a4\Omega(N)\geq 2\omega(N)+6a-4 and if Ω(m)K\Omega(m)\leq K then N<56(2K2a+11)2N< 5\cdot 6^{(2^{K-2a+1}-1)^2} where Ω(n)\Omega(n) and ω(n)\omega(n) denote the total number of prime factors and the number of distinct prime factors of the integer nn respectively.

Keywords

Cite

@article{arxiv.2404.00624,
  title  = {A note on necessary conditions for a friend of 10},
  author = {Tapas Chatterjee and Sagar Mandal and Sourav Mandal},
  journal= {arXiv preprint arXiv:2404.00624},
  year   = {2025}
}