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1 answer
186 views

Existence of Finite Amicable Groups

I'm interested in exploring the concept of "amicable groups" as follows: Definition. Two finite groups $G$ and $H$ are called amicable groups if: $G$ is the direct sum of proper subgroups ...
4 votes
1 answer
258 views

Density of numbers where a large prime factor satisfies a congruence

I am looking for an upper bound on the number of integers $n<x$ such that $n$ has a prime factor $p>\log(x)^{(1+\delta)}$ such that $p \equiv a \mod b$. Where $a,b$ are fixed and coprime and $0&...
1 vote
1 answer
221 views

Density of numbers with a large prime factor in specified arithmetic progression

I am looking for an answer to the following question. Fix some coprime integers $a$ and $b$ and let $S_x$ be the set of positive integers $n<x$ such that there exists a prime factor $p$ of $n$ with ...
0 votes
0 answers
102 views

On simple examples of unimodularity

$w=z=x+ 1 =y−1$ provides $wz−xy=w^2−(w−1)(w+ 1) = 1$. Hence if $x,y$ are odd then $w,z$ are even and all four integers are close. Is there elementary example where only $w$ is even and all four ...
4 votes
1 answer
336 views

Infinite, finitely generated linear group has indices of subgroups divisible by infinitely many primes

This question was previously asked at Math.SE, but didn't receive much attention. Let $G$ be an infinite finitely generated group and suppose that $G$ is linear, say $G \leq \operatorname{GL}_n(K)$ ...
8 votes
1 answer
575 views

Unstable Integers

There is a question that has been bothering my mind for quite a while now. I will present it and my current thoughts and progress on it. Let the prime factorization of an integer $n$ be $$n = p_1^{...
5 votes
1 answer
499 views

What is the asymptotic growth of $\sum_{k=1}^n 2^{\omega_k}$?

Question: Let $\omega_k$ be the number of distinct prime divisors of k. What is the asymptotic growth of $C_n := \sum_{k=1}^n 2^{\omega_k}$? Thank you for considering this elementary question. ...
1 vote
0 answers
274 views

Generalisation of the Liouville function as irreducible representations for the semigroup ($\mathbb{N},\cdot)$?

This is a duplicate of a question I have asked at here at math stack exchange, but I thought it could be also here of interest. When looking at the [Liouville function] (https://en.wikipedia.org/wiki/...
4 votes
0 answers
199 views

Linear combination of characters

For each $i \in \mathbb{N}$, let $G_{i}$ be a finite abelian group and $\widehat{G_{i}}$ the $\overline{\mathbb{Q}}$-valued character group of $G_{i}$. Suppose that $|G_{i}| \rightarrow \infty$ as $i \...
1 vote
2 answers
322 views

group theory behind the Kloosterman bound $| S(m,n;c) |< 2\, c^{3/4}$

I am trying to understand Kloosterman sums and their estimates (e.g. from [1], which does not prove) $$ \Big| S(m,n;c) \Big| = \Big| \sum_{(x,c) = 1} e\big( \frac{mx + nx^{-1}}{c}\big) \Big| < 2\, ...
5 votes
2 answers
832 views

Analogues of the Monster for central charges different from 24

One way to define the Monster group is to consider a conformal field theory (CFT) corresponding to central charge $c=24$ and look at the automorphism group of its vertex operator algebra. For one of ...
7 votes
3 answers
582 views

Asymptotics for the number of abelian groups of order at most $x.$

The number of abelian groups of order $n$ (call it $a(n)$ is a studied subject (see http://oeis.org/A000688), but I can't seem to find any asymptotic results. Obviously, there is no asymptotic for $a(...