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Questions on group theory which concern finite groups.
3
votes
Finite groups which have elements $g$ of order $pq$ such that the sizes of the conjugacy cla...
Yes, it trivially happens if $G = \langle g \rangle$ is the cyclic group
of order $pq$ -- then all $3$ conjugacy classes mentioned have precisely one element.
A smallest example of a nonabelian group …
7
votes
Accepted
Finite groups of order $n$ having exactly $n$ subgroups
There are finite groups of order $n$ having exactly $n$ subgroups
for $n = 1$, $2$, $6$, $8$, $28$, $36$, $40$, $40$, $48$, $54$, $72$,
$\dots$, and this list is exhaustive for $n < 96$.
The structure …
12
votes
Perfect group of order 190080
Just write
gap> G := PerfectGroup(IsPermGroup,190080);
M12 2^1
in order to get the desired group as a permutation group:
gap> GeneratorsOfGroup(G);
[ (3,6)(7,10)(9,12)(13,16)(15,18)(19,22)(20,23)( …
6
votes
Accepted
Finite solvable groups with abelian Fitting subgroup
The relation between supersolvability of a finite group and its Fitting
subgroup is that for a finite group $G$ the following are equivalent:
$G$ is supersolvable.
$G' \leq {\rm Fit}(G)$ and ${\rm F …
4
votes
0
answers
159
views
Can the numbers of elements of distinct prime orders of a finite simple group coincide? [duplicate]
Does there exist a finite simple group $G$ and distinct prime numbers
$p$ and $q$ dividing the order of $G$ such that the numbers of elements
of $G$ of order $p$ and $q$ are the same?
Remark 1: It ha …
3
votes
Equivalence classes of (2,3)-pairs in PSL(2,q)
While your observation is true also for ${\rm PSL}(2,7)$, ${\rm PSL}(2,8)$
and ${\rm PSL}(2,9)$, it is false for ${\rm PSL}(2,11)$. --
In ${\rm PSL}(2,11)$ there are two orbits of $(2,3)$-pairs whose …
9
votes
Accepted
Bounding from below the cardinality of a set of generators of the $n$-fold cartesian product...
The answer is no. -- For example, ${{\rm A}_5}^3$ is $2$-generated.
-- We have e.g.
$$
\langle (2,5)(3,4)(6,7,8,9,10)(11,12,15), (1,3,2,4,5)(6,7,9,10,8)(11,13,12,14,15) \rangle \ \cong \
{{\rm A}_ …
6
votes
About the number of their conjugacy classes in some classes of finite simple groups
No, in general the numbers of conjugacy classes of $B_n(q)$ and $C_n(q)$ differ -- for example, $B_3(3)$ has $58$ conjugacy classes, while $C_3(3)$ has $74$. This can be found easily with GAP:
gap> S …
4
votes
Accepted
Solvability of finite groups of order coprime to 15 -- proof without using CFSG?
As Derek Holt has pointed out, the answer to the question is yes. --
Thompson proved that the only finite simple groups of order coprime to 3 are the
Suzuki groups, and Glauberman later extended this …
4
votes
The Frattini subgroup of $D_{\infty}$
Put $a := xy$ and $b := y$. Then we have ${\rm D}_\infty = \langle a, b \rangle$. Clearly $a$ generates a subgroup of index 2, which is thus maximal. Also, given a prime $p$, the subgroup $G_p := \lan …
5
votes
Groups of order $p(p^2+1)/2$
For any constant $C \in \mathbb{N}$, there are infinitely many primes $p$
such that there are at least $C$ nonabelian groups of order $p(p^2+1)/2$:
Let $q \equiv 1$ mod $4$ be a prime, and $k \in \ma …
10
votes
Accepted
Finite groups for which the element orders form an arithmetic progression
No, your impression is not correct. -- A counterexample is the group ${\rm S}_5$, whose elements have orders $1, 2, 3, 4, 5$ and $6$.
As to groups with spectrum (i.e. set of element orders) equal to …
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 …
8
votes
1
answer
462
views
Solvability of finite groups of order coprime to 15 -- proof without using CFSG?
Is the solvability of finite groups of order coprime to 15
essentially easier to prove than the entire Classification of Finite Simple Groups?
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| …