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Questions about the branch of algebra that deals with groups.
7
votes
2
answers
403
views
Catalogue of groups with short finite presentations
For various types of groups, there exist catalogues of those groups of the
particular type which are "small" in a certain sense. — For example:
The GAP Small Groups Library catalogizes groups of smal …
11
votes
2
answers
738
views
How small can maximal subgroups be?
Given a finite group $G$, let $p(G)$ denote the number of prime factors
of the order of $G$ (counting multiplicities).
Does there exist a function $f: \mathbb{N} \rightarrow \mathbb{N}$
which grows fa …
32
votes
3
answers
3k
views
Order of products of elements in symmetric groups
Let $n \in \mathbb{N}$. Is it true that for any $a, b, c \in \mathbb{N}$ satisfying
$1 < a, b, c \leq n-2$ the symmetric group ${\rm S}_n$ has elements of order $a$ and $b$
whose product has order $c$ …
14
votes
2
answers
1k
views
Can a group generated by its involutions, the product of every two of which has order a powe...
Let $G$ be a group which is generated by the set of its involutions,
and assume that the product of every two involutions in $G$ has order
a power of 2. Is it possible that $G$ has an element of odd o …
6
votes
0
answers
196
views
Finite simple groups of "smooth" order
Given a finite group $G$, let $p(G)$ denote the largest prime factor
of the order of $G$. For the purpose of this question,
we say that the group $G$ has smooth order if its order exceeds
the order of …
3
votes
Estimate for the order of the outer automorphism group of a finite simple group
The order of a non-abelian finite simple group of order $n$ is bounded
by $_2\log(n)$, and this bound is sharp in the sense that it cannot be
improved by more than a small constant factor.
See A bound …
5
votes
2
answers
158
views
Quotients of a 2-generated dense subgroup of a Cartesian product of infinitely many finite a...
A "randomly chosen" 2-generated dense subgroup
$$
G \ = \ \langle a, b \rangle \ < \
{\rm A}_5 \times {\rm A}_6 \times {\rm A}_7 \times \dots
$$
of the cartesian direct product of the finite simpl …
2
votes
Orders of finite 2-simple groups
At least four such groups can share the same order:
$$
|{\rm A}_7 \times {\rm PSp}(6,2)| =
|{\rm PSU}(3,3) \times {\rm J}_2| =
|{\rm A}_8 \times {\rm A}_9| =
|{\rm PSL}(3,4) \times {\rm A}_9| …
5
votes
0
answers
135
views
The orders of which nonabelian finite simple groups can be written as products of other such...
Is it true that the order of a nonabelian finite simple group $G$ can be
written as the product of the orders of two or more other nonabelian
finite simple groups if and only if
$G$ is either an alte …
3
votes
Proving that a countable group is not finitely generated
One possible way of proving that a countable group $G$ is not finitely
generated is finding an infinite set $S$ and a mapping $\varphi$ from $G$
to the power set of $S$ such that the following hold:
…
6
votes
Group of exponential growth always contains a free sub-group?
Not necessarily. -- For example, the lamplighter group has exponential growth, but does not have a free subgroup of rank 2 (if $a$ and $b$ are two elements of that group of infinite order, then there …
4
votes
1
answer
193
views
Lower bound on size of largest conjugacy class of centreless perfect group
Problem 20.30 in the Kourovka Notebook asks whether the maximum size
of a conjugacy class of a perfect and centreless finite group $G$ is bounded below
by $|G|^{\frac{1}{2}}$. Clearly, there cannot be …
7
votes
Order of products of elements in symmetric groups
The question has meanwhile been answered in the positive in:
Joachim König, A note on the product of two permutations of prescribed orders.
European Journal of Combinatorics 57 (2016), 50-56.
The proo …
7
votes
0
answers
1k
views
Example of a group with unsolvable word problem
Today I noticed that the last relator in the 27-relator presentation
of a group with unsolvable word problem given in
Donald J. Collins: A simple presentation of a group with unsolvable word problem. …
4
votes
1
answer
150
views
Subgroups of finite simple groups $L(q^f)$ of Lie type normalized by $L(q)$
The following is a question asked to me these days by Gülin Ercan.
Let $G = L(q^f)$ be a finite simple group of Lie type,
and let $L(q) \cong H \le G$ be the group of fixed points
of the automorphisms …