{"title":"关于 20 岁之友的说明","authors":"Tapas Chatterjee, Sagar Mandal, Sourav Mandal","doi":"arxiv-2409.04451","DOIUrl":null,"url":null,"abstract":"Does $20$ have a friend? Or is it a solitary number? A folklore conjecture\nasserts that $20$ has no friends i.e. it is a solitary number. In this article,\nwe prove that, a friend $N$ of $20$ is of the form $N=2\\cdot5^{2a}m^2$ and it\nhas atleast six distinct prime divisors. Also we prove that $N$ must be atleast\n$2\\cdot 10^{12}$. Furthermore, we show that $\\Omega(N)\\geq 2\\omega(N)+6a-5$ and\nif $\\Omega(m)\\leq K$ then $N< 10\\cdot 6^{(2^{K-2a+3}-1)^2}$, where $\\Omega(n)$\nand $\\omega(n)$ denote the total number of prime divisors and the number of\ndistinct prime divisors of the integer $n$ respectively. In addition, we deduce\nthat, not all exponents of odd prime divisors of friend $N$ of $20$ are\ncongruent to $-1$ modulo $f$, where $f$ is the order of $5$ in\n$(\\mathbb{Z}/p\\mathbb{Z})^\\times$ such that $3\\mid f$ and $p$ is a prime\ncongruent to $1$ modulo $6$.","PeriodicalId":501502,"journal":{"name":"arXiv - MATH - General Mathematics","volume":"36 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"A note on friends of 20\",\"authors\":\"Tapas Chatterjee, Sagar Mandal, Sourav Mandal\",\"doi\":\"arxiv-2409.04451\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Does $20$ have a friend? Or is it a solitary number? A folklore conjecture\\nasserts that $20$ has no friends i.e. it is a solitary number. In this article,\\nwe prove that, a friend $N$ of $20$ is of the form $N=2\\\\cdot5^{2a}m^2$ and it\\nhas atleast six distinct prime divisors. Also we prove that $N$ must be atleast\\n$2\\\\cdot 10^{12}$. Furthermore, we show that $\\\\Omega(N)\\\\geq 2\\\\omega(N)+6a-5$ and\\nif $\\\\Omega(m)\\\\leq K$ then $N< 10\\\\cdot 6^{(2^{K-2a+3}-1)^2}$, where $\\\\Omega(n)$\\nand $\\\\omega(n)$ denote the total number of prime divisors and the number of\\ndistinct prime divisors of the integer $n$ respectively. In addition, we deduce\\nthat, not all exponents of odd prime divisors of friend $N$ of $20$ are\\ncongruent to $-1$ modulo $f$, where $f$ is the order of $5$ in\\n$(\\\\mathbb{Z}/p\\\\mathbb{Z})^\\\\times$ such that $3\\\\mid f$ and $p$ is a prime\\ncongruent to $1$ modulo $6$.\",\"PeriodicalId\":501502,\"journal\":{\"name\":\"arXiv - MATH - General Mathematics\",\"volume\":\"36 1\",\"pages\":\"\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2024-08-25\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"arXiv - MATH - General Mathematics\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/arxiv-2409.04451\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"arXiv - MATH - General Mathematics","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/arxiv-2409.04451","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
Does $20$ have a friend? Or is it a solitary number? A folklore conjecture
asserts that $20$ has no friends i.e. it is a solitary number. In this article,
we prove that, a friend $N$ of $20$ is of the form $N=2\cdot5^{2a}m^2$ and it
has atleast six distinct prime divisors. Also we prove that $N$ must be atleast
$2\cdot 10^{12}$. Furthermore, we show that $\Omega(N)\geq 2\omega(N)+6a-5$ and
if $\Omega(m)\leq K$ then $N< 10\cdot 6^{(2^{K-2a+3}-1)^2}$, where $\Omega(n)$
and $\omega(n)$ denote the total number of prime divisors and the number of
distinct prime divisors of the integer $n$ respectively. In addition, we deduce
that, not all exponents of odd prime divisors of friend $N$ of $20$ are
congruent to $-1$ modulo $f$, where $f$ is the order of $5$ in
$(\mathbb{Z}/p\mathbb{Z})^\times$ such that $3\mid f$ and $p$ is a prime
congruent to $1$ modulo $6$.