Proving the Order of the Symmetric Group S_N: Where to Begin?

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In summary, to prove that the symmetric group S_N is of order N!, one must construct a bijection of {1, 2, ..., n-1, n} onto itself, with n choices for the first element and n-1 for the second element, and so on. This results in N! possible permutations, showing that S_N is of order N!.
  • #1
bjogae
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Homework Statement



Show that the symmetric group (permutation group) S_N is of order N!

Homework Equations





The Attempt at a Solution



I can't get started on how to prove this. I understand that if

n=2 S_2= {E, (12)}
n=3 S_3={E, (12), (13), (23), (123), (132)}

and so on. This makes this seem kind of intuitive. However I can't even get started on proving it for N. Could somebody please help me get started?
 
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  • #2
Given {1, 2, ..., n-1, n}, you want to construct a bijection onto itself. So take the first element, 1. There are n choices of elements it can map to. Then consider 2. There are n-1 elements it can map to (since the function is 1-1 and one of the n elements is already 'taken' by 1)
 
  • #3
Got it. Thanks.
 

Related to Proving the Order of the Symmetric Group S_N: Where to Begin?

What does it mean for a group to be of order N?

For a group to be of order N means that it has N elements. This is also referred to as the group's cardinality or size.

What is the significance of showing that S_N is of order N?

Showing that S_N is of order N is important because it helps us understand the structure and properties of symmetric groups. It also allows us to make connections between different mathematical concepts and applications.

How can one prove that S_N is of order N?

To prove that S_N is of order N, one can use the definition of symmetric groups and show that it contains N elements. This can be done through various methods, such as constructing the group's multiplication table or using mathematical induction.

What are some real-world applications of understanding the order of symmetric groups?

Understanding the order of symmetric groups has many practical applications in fields such as cryptography, combinatorics, and physics. For example, in cryptography, symmetric groups are used in the development of secure encryption algorithms.

Can S_N be of order other than N?

No, S_N can only be of order N. This is because the number of elements in a symmetric group is directly related to the number of elements in the set that it is permuting, which is always N in the case of S_N.

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