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Questions about the branch of algebra that deals with groups.
47
votes
1
answer
2k
views
Transitivity on $\mathbb{N}_0$ -- a 42 problem
Let $r(m)$ denote the residue class $r+m\mathbb{Z}$, where $0 \leq r < m$.
Given disjoint residue classes $r_1(m_1)$ and $r_2(m_2)$, let the class
transposition $\tau_{r_1(m_1),r_2(m_2)}$ be the permu …
33
votes
2
answers
1k
views
Richness of the subgroup structure of p-groups
Given a prime $p$ and $n \in \mathbb{N}$, let $f_p(n)$ be the smallest
number such that there is a group of order $p^{f_p(n)}$ which all groups of
order $p^n$ embed into. What is the asymptotic growth …
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 $c$ …
30
votes
2
answers
2k
views
Fractal-like structures arising from the action of a group on $\mathbb{Z}^2$
Let $G := \langle a, b, c \rangle < {\rm Sym}(\mathbb{Z}^2)$ be the group
generated by the permutation
$$
a: \ (m,n) \ \mapsto \ (m-n,m)
$$
of order $6$ and the involutions
$$
b: \ (m,n) \ \mapsto …
27
votes
Are there $n$ groups of order $n$ for some $n>1$?
A "near-miss" is $N(19328) = 19324$, while the only $n \leq 2000$
such that $|N(n)-n| \leq 25$ are $1$, $2$, $3$, $4$, $5$, $6$, $7$, $8$,
$9$, $10$, $11$, $12$, $13$, $14$, $15$, $16$, $17$, $18$, $1 …
22
votes
1
answer
1k
views
Numbers of distinct products obtained by permuting the factors
Let $n \in \mathbb{N}$. Is it true that for every $k \in \{1, \dots, n!\}$ there are
some group $G$ and pairwise distinct elements $g_1, \dots, g_n \in G$ such that the set
$\{g_{\sigma(1)} \cdot \ \d …
22
votes
Small-index subgroups of SL(3,Z)
In order to answer the question we need a finite presentation
of ${\rm SL}(3,\mathbb{Z})$ and a general method to find all subgroups of index
$\leq n$ of a finitely presented group:
A finite present …
21
votes
3
answers
930
views
Primes occurring as orders of elements of a finitely presented group
Is it true that given a finitely presented group $G$, either all primes
or only finitely many of them occur as orders of elements of $G$?
21
votes
1
answer
562
views
Partitions of ${\rm Sym}(\mathbb{N})$ induced by convergent, but not absolutely convergent s...
Let $(a_n) \subset \mathbb{R}$ be a sequence such that the series
$\sum_{n=1}^\infty a_n$ converges, but does not converge absolutely.
Then there is a partition of the symmetric group ${\rm Sym}(\math …
18
votes
Why do sporadic simple groups have so few conjugacy classes?
This is also rather an expanded comment. --
Since for purely arithmetical reasons, $\ln(\ln(|G|))$ is a lower bound
for the number $k(G)$ of conjugacy classes of a finite group $G$, maybe
$$
f(G) := …
17
votes
Is there an infinite group with exactly two conjugacy classes?
The answer to the question is yes, even if one
additionally requires the group to be finitely generated.
In this case, the question is Problem 9.10 in the Kourovka Notebook,
and has been answered in: …
17
votes
0
answers
965
views
Groups generated by 3 involutions
Let $r(m)$ denote the residue class $r+m\mathbb{Z}$, where $0 \leq r < m$.
Given disjoint residue classes $r_1(m_1)$ and $r_2(m_2)$, let the class transposition
$\tau_{r_1(m_1),r_2(m_2)}$ be the permu …
16
votes
1
answer
913
views
Is it true that every f.g. infinite simple group has exponential growth?
Is it true that every finitely generated infinite simple group has
exponential (word-)growth?
Remark: As Mark Sapir has pointed out, the question whether
every finitely generated group of subexponent …
16
votes
Conjugacy classes of $\mathrm{SL}_2(\mathbb{Z})$
The conjugacy classes of elements of ${\rm SL}(2,\mathbb{Z})$
with given trace are counted in:
S. Chowla, J. Cowles and M. Cowles:
On the number of conjugacy classes in SL(2,Z).
Journal of Number …
15
votes
1
answer
1k
views
Free subgroups of $\mathrm{GL}(2,\mathbb{Z})$
Is there a bound $B$ such that every 2-generator subgroup
$G = \langle a, b \rangle \le {\rm GL}(2,\mathbb{Z})$
whose generators do not satisfy a relation of length $\leq B$ is free?
If it exists, su …