Proving converse of fundamental theorem of cyclic groups

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SUMMARY

The discussion centers on proving that a finite abelian group G is cyclic if it has exactly one subgroup of order d for every divisor d of the order of G. Participants clarify that the example of C_2 x C_2 is invalid because it contains multiple subgroups of order 2, contradicting the requirement for uniqueness. The emphasis is on the necessity of having precisely one subgroup for each divisor, which is crucial for the proof.

PREREQUISITES
  • Understanding of finite abelian groups
  • Knowledge of group order and subgroups
  • Familiarity with the fundamental theorem of cyclic groups
  • Basic concepts of group theory
NEXT STEPS
  • Study the structure of finite abelian groups
  • Learn about subgroup lattice and its implications
  • Explore the proof of the fundamental theorem of cyclic groups
  • Investigate examples of groups with unique subgroup orders
USEFUL FOR

Mathematics students, particularly those studying abstract algebra, group theorists, and anyone interested in the properties of finite abelian groups.

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Homework Statement


If G is a finite abelian group that has one subgroup of order d for every divisor d of the order of G. Prove that G is cyclic.


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The Attempt at a Solution

 
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Post what you've done on this problem please.
 
Can you check the question. C_2 x C_2 has subgroups of orders 1,2 and 4, but is not cyclic.
 
matt grime said:
Can you check the question. C_2 x C_2 has subgroups of orders 1,2 and 4, but is not cyclic.

I think the point is that it is supposed to have ONE subgroup of each order. Your example has several subgroups of order 2.
 
And that's why we have the word 'exactly'.
 

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