Can the Direct Sum of Cyclic Groups Determine the Properties of Finite Groups?

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Discussion Overview

The discussion revolves around the properties of finite groups, specifically whether the direct sum of cyclic groups can determine characteristics such as being cyclic or abelian. Participants explore the implications of the order of elements and the structure of groups, including examples like the symmetric group S_3.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes that if G is a finite group and H consists of elements that equal the identity for some n, then H has at most n elements if G is cyclic.
  • Another participant questions whether it is possible to add an element to G without adding it to H, suggesting that every element must equal the identity for some n.
  • A participant references the nonabelian group D_3 (S_3) and discusses its elements of order 3, questioning the implications for H.
  • There is a suggestion that the treatment of n as both a constant and a variable may lead to confusion regarding the properties of H.
  • One participant emphasizes the need to clarify whether the statement about H applies "for all n" or for specific values of n.
  • Another participant expresses uncertainty about the implications of H having fewer elements than expected based on the orders of elements in S_3.
  • There is a proposal to consider the direct sum of cyclic groups of various orders to investigate the presence of elements of a specific order.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between the properties of G and H, with no consensus reached on whether the conditions on H can definitively determine if G is cyclic or abelian.

Contextual Notes

Participants note potential confusion regarding the treatment of n, the dependence on specific definitions of H, and the implications of group structure on the properties being discussed.

Zaare
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Assume G is a finite group and H = \left\{ {g \in G|g^n = e} \right\} for any n>0. e is identity.
I have been able to show that if G is cyclic, then H has at most n elements.
However, I can't go the other way. That is, assuming H has at most n elements, I haven't been able to say anything about whether G is cyclic, abelian or neither.
Any suggestions?
 
Last edited:
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Can you add an element to G without adding an element to H?
 
Look at D_3=S_3 the nonabelian group of order 6. How many elements of order 3 does it have?
 
Can you add an element to G without adding an element to H?
Since G is a finite group, then every element in G must equal identity for some n. That means that for some n the element must be added to H. So I think the answer is no. But I can't make any connection to my problem.

Look at D_3=S_3 the nonabelian group of order 6. How many elements of order 3 does it have?
If I haven't made any mistakes, it has 2 elements of order 3 and 3 elements of order 2. But that means that H has 3 elements for n=2 (which does not agree with the assumption that H has at most n elements), doesn't it?

I'm quite confused now...
 
You seem to be treating n as both a constant and a variable -- that might be the source of confusion.
 
I don't mean to treat n as a variable, only as an unknown constant. Where do I treat it as a variable?
 
"Since G is a finite group, then every element in G must equal identity for some n. That means that for some n the element must be added to H."
 
S_3 is a group that has fewer than 3 elements of order 3. How does that not prove useful unless you're being odd about n: at least quantify it: there exists an n, or "for all n".

It apparently seems you wish it to be "for all n", which you didn't bother to specify.
 
But a certain value of n defines a certain H, so I have to consider the different values n can take.

What I mean is for any n.
 
  • #10
So, what you want to prove (or disprove) is that if:

For all n > 0, Hn has no more than n elements

Then G is cyclic?
 
  • #11
Yes, and if it's not cyclic: Is it "at least" abelian?

I'm sorry about the poor specification.
 
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  • #12
try the direct sum of the cyclic groups of orders 2,3,5,7,11,13,17,19,23,29. and look for elements of order 2.
 

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