Isomorphism between Dihedral and Symmetric groups of the same order?

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SUMMARY

The Dihedral group Dn (or D2n) and its corresponding Symmetric group Sn are not isomorphic for groups of the same order, as established in the discussion. Specifically, Dn has 2n elements, while Sn has n! elements, leading to a fundamental difference in their structures. The example of D3 (or D6) and S3 illustrates that while they can be isomorphic, this is not a general rule. The symmetry of shapes, such as triangles and squares, further demonstrates that not all permutations correspond to elements in the Dihedral group.

PREREQUISITES
  • Understanding of group theory concepts, specifically Dihedral groups and Symmetric groups.
  • Familiarity with the definitions of isomorphism and homomorphism in the context of algebraic structures.
  • Knowledge of the properties of permutations and their relation to symmetry.
  • Basic comprehension of the factorial function and its implications in counting elements in groups.
NEXT STEPS
  • Study the properties of Dihedral groups Dn and their applications in geometry.
  • Learn about the structure and properties of Symmetric groups Sn, focusing on their element counts and permutations.
  • Explore the concept of group isomorphism in greater depth, including bijective homomorphisms.
  • Investigate specific examples of groups that are isomorphic and non-isomorphic to solidify understanding.
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Mathematicians, students of abstract algebra, and anyone interested in the relationships between different algebraic structures, particularly in the context of group theory.

Bleys
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Is there a way to prove generally that the Dihedral group and its corresponding Symmetric group of the same order are isormorphic. In class we were only shown a particular example, D3 (or D6 whatever you wish to use) and S3, and a contructed homomorphism, but how could you do it generally? Would you still have to construct a specific map and show that it's a bijective homomorphism? Or can you just simply show there exists at least one isomorphic map between the two?
 
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They are not. In general, Dn (or D2n) has 2n elements, whereas Sn has n!.

Of course, the reason that it works for the triangle group, is that any permutation of its vertices is also a symmetry. However, the permutation group for the vertices of a square is already larger than its symmetry group. For example: if you label the corners 1, 2, 3, 4 in clockwise order, then the symmetry that interchanges 1 with 3 and 2 with 4 does not correspond to any element from D4 (or D8).
 

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