Carmichael numbers and least common multiples of $p-1$

TL;DR

This paper investigates Carmichael numbers with a fixed gcd of prime minus one factors, establishing lower bounds on their distribution under a conjecture, revealing new structural insights into their composition.

Contribution

It introduces a novel approach to analyze Carmichael numbers with fixed gcd of prime factors, providing lower bounds under a conjecture, contrasting with traditional constructions.

Findings

Lower bounds on the count of Carmichael numbers with fixed gcd of prime factors.

Demonstrates existence of many such Carmichael numbers under a conjecture.

Highlights a new structural perspective on Carmichael numbers.

Abstract

For a Carmichael number $n$ with prime factors $p_1,\cdots,p_m$, define $$K=GCD[p_1-1,\cdots,p_m-1],$$ and let $C_\nu(X)$ denote the number of Carmichael numbers up to $X$ such that $K=\nu$. Assuming a strong conjecture on the first prime in an arithmetic progression, we prove that for any even natural number $\nu$, $$C_\nu(X)\geq X^{1-(2+o(1))\frac{\log\log\log \log X}{\log\log\log X}}.$$ This is a departure from standard constructions of Carmichael numbers, which generally require $K$ to grow along with $n$.