Algebra and Permutations: Determining the Parity of an Element in S_n

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SUMMARY

The discussion centers on determining the parity of a permutation σ in the symmetric group S_n, given that σ^5 equals the identity permutation. It is established that since the identity permutation is even, σ must also be even. The key equation used is Parity(σ) = (∑_{i=1}^k(|c_i|-1)) mod 2, which relates the cycle structure of σ to its parity. The conclusion drawn is that if σ^5 = 1, σ cannot be an odd permutation.

PREREQUISITES
  • Understanding of symmetric groups, specifically S_n
  • Knowledge of permutation cycles and their properties
  • Familiarity with the concept of parity in permutations
  • Basic algebraic manipulation and modular arithmetic
NEXT STEPS
  • Study the properties of cycle decompositions in permutations
  • Learn about the relationship between permutation orders and parity
  • Explore advanced topics in group theory, focusing on symmetric groups
  • Investigate examples of permutations in S_n and their cycle structures
USEFUL FOR

Mathematics students, particularly those studying abstract algebra, group theory, and combinatorics, as well as educators teaching these concepts.

decerto
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Homework Statement



Suppose σ is an element of S_n, if σ^5=1, is σ necessarily odd or even

Homework Equations



Parity(\sigma)= (\sum_{i=1}^k(|c_i|-1)) mod 2

The Attempt at a Solution



Really unsure how to even start this, I think I have to use the fact you can decompose every permutation into a product of disjoint or 2 cycles and use their properties to show in what cases it's even or odd but I'm not really sure.
 
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decerto said:

Homework Statement



Suppose σ is an element of S_n, if σ^5=1, is σ necessarily odd or even

Homework Equations



Parity(\sigma)= (\sum_{i=1}^k(|c_i|-1)) mod 2

The Attempt at a Solution



Really unsure how to even start this, I think I have to use the fact you can decompose every permutation into a product of disjoint or 2 cycles and use their properties to show in what cases it's even or odd but I'm not really sure.

##\sigma^5=\sigma \sigma \sigma \sigma \sigma=1##. ##1## is an even permutation. Suppose ##\sigma## were odd. Then what would be the parity of ##\sigma^5##?
 
What does σ5 being even tell you?
 
Last edited:

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