Use with the (group-theory) tag. A group is cyclic if it can be generated by a single element, $a$. Every element has the form $a^i$ for some $i\in\mathbb{Z}$, and so these groups are abelian.

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1answer
17 views

Verify that $A \oplus B$, where $A$ and $B$ are cyclic groups of orders 2 and 3, is the cyclic group of order 6

Let's define $A$ and $B$ as follows: $A$ = {e,a} $B$ = {e,b,2b} Then $A\oplus B= \{\{e+e\},\{e+b\},\{e+2b\},\{a+e\},\{a+b\},\{a+2b\}\}$ which is equal to ...
2
votes
1answer
51 views

Every group of order $35$ is cyclic? [duplicate]

Prove that every group of order $35$ is cyclic. Now, the subgroups of this are ones whose orders divide the order of this group(by lagrange), these are of prime orders $7$ and $5$. and I guess ...
2
votes
3answers
45 views

If $H$ and $K$ are subgroups of $G$ whose orders are coprime. Is $H\cap K$ a subgroup of $H$ and $K$?

If $H$ and $K$ are subgroups of $G$ whose orders are coprime. Is $H\cap K$ a subgroup of $H$ and $K$? They both have the same identity, so we know at minimum we have $\{e\}$ so it is the trivial ...
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1answer
18 views

The generators of the group $\langle\mathbb{Z}_n,\oplus\rangle$ are all $g \in \mathbb{Z}_n $ for which $\gcd(g,n)=1$ [duplicate]

I'm trying to find a proof of this: The group $\langle\mathbb{Z}_n,\oplus\rangle$ is cyclic for every $n$, where $1$ is a generator. The generators of the group ...
2
votes
2answers
69 views

Proof to a property of Euler's totient function

The property is $$\sum_{d|n}\phi(d) = n$$ And the proof provided is If $d$ divides $n$, let $C_d$ be the unique subgroup of $\mathbb{Z}/n\mathbb{Z}$ of order $d$, and let $\Phi_d$ be the set of ...
2
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0answers
58 views

Does group $G$ of order 42 have a normal cyclic subgroup of order 21?

Show that a group $G$ of order 42 has a normal cyclic subgroup of order 21. What I did so far is using Sylow's theorem to show that $G$ has a unique 7-sylow subgroup $S(7)$ (which is normal) and {1 ...
0
votes
2answers
13 views

How do you find the order of a cyclic group?

What is the order of the cyclic group generated by $(1 2 5)(3 4)$? What is the order of the cyclic group generated by $(1 2 5)(3 5)$? I've looked through my notes and can't find notes on this and can ...
0
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1answer
37 views

Order of a cyclic group?

When finding the order of a cyclic group, do we determine so by counting the number of elements in that group generator by the cyclic group?
0
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1answer
86 views

In $(\mathbf Z/p^r \mathbf Z)^*$, finding an element with order $p-1$.

Let $p$ be an odd prime number. I want to prove that $(\mathbf Z/p^r \mathbf Z)^*$ is an cyclic group. I have known that $\overline {p-1} \in (\mathbf Z/p^r \mathbf Z)^*$ is of order $p^{r-1}$. Since ...
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4answers
41 views

If $G = \langle a\rangle$ and $b$ $\in$ $G$, the order of $b$ is a factor of the order of $a$

Prof. Pinter's "A Book of Abstract Algebra" presents the following exercise from the "Cyclic Groups" chapter: If $G = \langle a\rangle$ is finite and $b$ $\in$ $G$, the order of $b$ is a factor ...
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1answer
23 views

List of the Elements of $(1 \rightarrow 6,2 \rightarrow 1, 3 \rightarrow 3, 4 \rightarrow 2, 5 \rightarrow 5, 6 \rightarrow 4)$

Dr. Pinter's A Book of Abstract Algebra presents the following exercise in the "Cyclic Groups" chapter. List the elements of $\langle f\rangle$ in $S_6$ where $f$ = $$(1 \rightarrow 6,2 ...
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3answers
30 views

Proof: Every Cyclic Group is Abelian

Dr. Pinter's "A Book of Abstract Algebra"'s chapter on Cyclic Groups presents the exercise: Prove that every cyclic group is abelian. Here's my attempt: By Theorem 1 (of this chapter): ...
1
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1answer
30 views

Correctness of proof of generalized Euler's criterion

My lecture notes on quadratic residues were pretty sloppy, and I was trying to prove some theorems from class. I don't think I'm correct, though. Can anyone tell me if I'm wrong? Specifically, I think ...
3
votes
2answers
69 views

Abstract Algebra: Every group has a cyclic subgroup

I have to show that every group has a cyclic subgroup. I know what this means, and to me it is obvious, yet I am not sure how to formally write it. I proved it directly, as follows: Let G be a ...
1
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1answer
40 views

under following conditions $G$ has only one subgroup of order $p$.

Let $|G|=p^m$ for $m \ge 2$. If every subgroup of $G$ of order $p^2$ is cyclic, then $G$ has only one subgroup of order $p$.
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4answers
126 views

A finite group which has a unique subgroup of order $d$ for each $d\mid n$.

Problem Suppose G is a finite group of order $n$ which has a unique subgroup of order $d$ for each $d\mid n$. Prove that $G$ must be a cyclic group. My idea: I try to prove it by induction. Let ...
2
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1answer
34 views

Is there any cyclic subgroup of order 6 in in $ S_6$?

Is there any cyclic subgroup of order 6 in $ S_6$? Attempt: $|S_6|=6!=720$ Let $H$ be a subgroup of $S_6$ ,$H$ cyclic $\iff\langle H \rangle=\{e,h,h^2,...,h^{n-1}\}=S_6$
0
votes
2answers
80 views

Abelian group which is not one of these

Im struggling to find a finite abelian (commutative , associative) group $(G,\circ)$ with some specific conditions: $a\circ b$ isn't naive addition $a+b$ for $a,b\in G$ $G$ is a subset of ...
2
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1answer
29 views

Cyclic consecutive zeros of binary sequence with prime length

I found a feature that if $N>5$ is a prime, and $M \triangleq \frac{N-1}{2}$ is also a prime, then we will always have a binary sequence $x_1,\ldots, x_N$ with $L=\frac{N-1}{2}$(or ...
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5answers
135 views

If $G$ is cyclic then $G/H$ is cyclic?

If $G$ is cyclic, then $G/H$ is cyclic? The proof I got goes like this: $G$ is cyclic, so $G=<g>$ for some $g\in G$. So any coset in $G/H$ would be of the form $Hg'=Hg^n$ for some $n$. So ...
1
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1answer
23 views

Find the Existence and Uniqueness of a Cyclic subgroup

Giving that $|H|$ is cyclic. If $|H|=n$ then for each $a>0$ such that $a|n$ there exist a unique subgroup of $H$ of order $a$. This subgroup is Cyclic subgroup $\langle x^d\rangle$ where $d= ...
0
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2answers
43 views

Cyclic groups and other groups

Ok So I know that a cyclic group is a group that is generated by a single element like $\large{(Z_n,+)}$. Now I was wondering that if every group has a generator , and I found that the answer is yes ...
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0answers
31 views

Writing a group as a product of cyclic groups

How do I go about expressing a group as a product of cyclic groups? For example, express: $$O^*_K = \{\pm (24 + 5\sqrt{23})^r : r\in \mathbb{Z} \}$$ as a product of cyclic groups ($O^*_K$ is the ...
2
votes
3answers
42 views

Isomorphism of a product $C_n \times C_m$ of cyclic groups with the cyclic group $C_{mn}$

Given that $C_n$ is a cyclic group of order $n$, what conditions must integers $n$ and $m$ satisfy such that the group $C_n \times C_m$ is isomorphic to C$_{mn}$? So I attempted to investigate a ...
0
votes
1answer
63 views

$g$ has order $n$, then $\langle g\rangle=\langle g^2\rangle=\cdots=\langle g^{n-1}\rangle$

If $g$ has order $n$, then $\langle g\rangle=\langle g^2\rangle=\cdots=\langle g^{n-1}\rangle$. This should be fairly easy but somehow I just couldn't prove it. I only managed to prove the case ...
1
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1answer
32 views

Groups and Subgroups elements

Let $G$ be a cyclic group order $12$ with $G=\left<a\right>$. Let $H=\left<a^3\right>$. List the elements of $H$ and find the cosets. I am lost as to what the elements of $H$ would be. ...
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2answers
66 views

$|G|=p_1p_2p_3$ distinct primes with $p_i \nmid p_j-1$ then $G$ is cyclic

Problem Let $p_1,p_2,p_3$ be three distinct primes with $p_i \nmid p_j-1$ for all $1\leq i,j \leq 3$ and let $G$ be a group of order $p_1p_2p_3$. Show that $G$ is cyclic. I've tried to come up with ...
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1answer
41 views

Is the direct product $\Bbb Z \times \Bbb Z$ with operation $(n,m)+(p,q):=(n+p,m+q)$ a cyclic group?

Is the direct product $\Bbb Z \times \Bbb Z$ with operation $(n,m)+(p,q):=(n+p,m+q)$ a cyclic group? I know its not a cyclic group but how would i show this in a formal way?
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1answer
47 views

What are all the subgroups of $\Bbb{Z}/10\Bbb{Z}$?

I thought they would be $\Bbb{Z}/n\Bbb{Z}$, where $1 \leq n \leq 10 $. What is wrong in that ? And, how is $\Bbb{Z}/n\Bbb{Z}$ a cyclic group. Is it's generator the element 1 ?
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0answers
34 views

Clarification for question: Homomorphisms from $\Bbb Z / n \to \Bbb C_{\ne 0}$

Please don't solve the problem - it is for an assignment - this is just a question for clarification purposes. Let $G$ be a group and $\hat G$ be the set of homomorphisms from $G$ to the group of ...
3
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1answer
36 views

Is a finite cyclic group a Poincare duality group?

I am trying to understand whether the finite cyclic group of order $n$, $C_n$ is a Poincare duality group, i.e. whether it's classifying space $K(C_n,\,1)$ is a Poincare complex. I know that the ...
5
votes
2answers
74 views

Help to prove that $ U_{p} $ is a cyclic group.

As part of my study of Abstract Algebra, I’m trying to prove that $ U_{p} $ is cyclic for $ p $ a prime number. It’s a classical result, but I’m trying to prove it following four steps stated as ...
1
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1answer
25 views

Group theory disjoint cycles

Let $a=(1 3 5)(1 5 6)(1 3 5)$ I had to write this as a product of disjoint cycles and got $(1 5)(3 6)$ which I believe is correct. Then figure out $a^{24}$ and $a^{25}$. Now $a^{24}$ is the ...
7
votes
2answers
632 views

Why is the set of integers with the operation of addition considered a cyclic group?

The first sentence in the Wikipedia article entitled "Cyclic Groups" states that "In algebra, a cyclic group is a group that is generated by a single element". How is this consistent with addition on ...
2
votes
1answer
28 views

Looking for different proofs for $-1$ is a quadratic residue of primes of the form $4k+1$ and related facts

Suppose $p$ is a prime of the form $4k+1$ , then $4|p-1=|\mathbb Z_p^*|$ , as $\mathbb Z^*_p$ is a cyclic group , so there is $\bar x \in \mathbb Z_p^*$ such that $o(\bar x)=4$ , then $o(\bar x^2)=2$ ...
1
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1answer
69 views

Quotient group(Factor group)

Prove that the quotient group $\frac{Z\times Z\times Z}{<(1,1,1)>}$ is an infinite, non-cyclic group. Here Z is the group of integers with operation of addition, $<(1,1,1)$> is the ...
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votes
1answer
37 views

Subgroup of a cyclic finite group [closed]

Let $G$ be a cyclic group of order $n$ and let $m$ be a positive integer dividing $n$. Show that $G$ contains one and only subgroup of order $m$. I have started the proof by stating the smallest ...
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2answers
42 views

Is $\mathbb{Z}\times\mathbb{Z}/((6,5),(3,4))$ is finitely generated?

Let $A$ be the quotient of the free abelian group $\mathbb{Z}^2$ by the subgroup generated by $(6,5)$ and $(3,4)$. the question is $A$ is finitely generated? and if Yes. Can we Decompose it into a ...
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0answers
21 views

Question about exponents of groups

Okay, I'm trying to understand exponents of groups. I will start with the Set Z_3, where Z_3 is the integers mod3 under addition. Now, I want to set out to find the exponent of this group, but ...
1
vote
2answers
56 views

Can a cyclic group have more than two generators? [duplicate]

Can a cyclic group have more than two generators? for example the group $\mathrm{Z}$ has two generators $-1$ and $1$, but can a group have more than two generators?
1
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1answer
39 views

Generating elements of large group of units of a field.

Suppose $F$ is a large but finite field, and $F^\text{x}$ is the group of non-zero elements of the field. It is known that this group is always cyclic, and we could ask a natural question "what are ...
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2answers
29 views

Do Equal Sets Have the Same Enumerations?

One of the first proofs in group theory is to show that in a finite $G$, the order of the element $g$ is the same as the order of the subgroup $\langle g \rangle$. Let the order of $g$ equal $m$. ...
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0answers
20 views

Multiple maximal cyclic subgroups of a symmetry group

If a symmetry group T has a maximal cyclic subgroup Cn because of a projection I1, then it means it will have a rotational symmetry order of n. If we have another projection (of the same object) with ...
1
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1answer
37 views

How many cycles $A$ and $B$ can form this cycle

How many cycles $A$ and $B$ can form this cycle: $AB=(axyguimjrcwk)(bvqphsleofzt)(d)(n)$ I can see that $A$ and $B$ must share the cycle $(dn)$, and I believe due to ordering, both $A$ and $B$ must ...
0
votes
1answer
43 views

How do I prove that there exists a cyclic subgroup of order lcm of orders of cyclic subgrpups of an abelian group?

Before I start, please note that this post is not duplicate Let $G$ be an abelian group. Let $H,K$ be finite cyclic subgroups of $G$ such that $|H|=r,|K|=s$. Then, how do I prove that there exists ...
1
vote
1answer
41 views

Is $A_n$ isomorphic to $C_n$ in general

Let $A_n$ denote the alternating group of order $n$, and let $C_n$ be the cyclic group of order $n$. Correct me if I'm wrong, but I know that $A_3 = \{(),(1,2,3),(1,3,2)\}\cong \{0,1,2\}=C_3$. I'm not ...
3
votes
0answers
65 views

prove that a is of order m if and only if $a^m = e$ and $a^k $is not $e$ for all $0 < k < m$.

$a$ is of order $m$ if and only if $a^m = e$ and $a^k \neq e$ for all $0 < k < m$. It is about order in Algebra. I sketch the proof. Is it correct? I need your help. First ($\Rightarrow$) Let ...
0
votes
1answer
45 views

Finding subgroups of order $4$ of $\mathbb{Z}_2\times\mathbb{Z}_4$

Now, the question asks me what the subgroups of order $4$ are of this relation and then to give them as sets and identify the group of order $4$ that each of the subgroups is isomorphic to. How do I ...
0
votes
0answers
47 views

How to tell if a directed graph has a cycle?

If I have the directed graph here: I am confused whether or not this is a cycle or not. Because in the underlying graph, this is a 3-cycle for sure, but in the directed graph, there is no cycle if ...
0
votes
1answer
43 views

Group Theory - Cyclic Groups & Direct Product

Prove that if $G$ is an infinite group and $H$ is a group then $G \times H$ is cyclic if and only if $G$ is cyclic a $H =$ {${e_H}$}. Solution: I can see that this is true but I don't know how to ...