Understanding Aut(Aut(Aut(C_73))) in Group Theory

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SUMMARY

The discussion focuses on calculating the automorphism group Aut(Aut(Aut(C_{73}))). The conclusion reached is that Aut(Aut(Aut(C_{73}))) is isomorphic to Aut(C_2 × C_2 × C_2) × Aut(C_3), which further simplifies to GL_3(ℱ_2). The participants clarify that Aut(C_{73}) equals U(73), which is isomorphic to C_{72}, and that Aut(C_{72}) can be expressed as U(72) = U(2^3) × U(3^2) = C_2 × C_2 × C_2 × C_2 × C_3. A correction is made regarding the factors involved in the automorphism calculations.

PREREQUISITES
  • Understanding of group theory concepts, specifically automorphism groups.
  • Familiarity with the structure of cyclic groups, such as C_{73} and C_2.
  • Knowledge of the unit group notation, U(n), and its properties.
  • Basic understanding of linear algebra, particularly the general linear group GL_n over finite fields.
NEXT STEPS
  • Study the properties of automorphism groups in group theory.
  • Learn about the structure and properties of the unit group U(n) for various n.
  • Research the general linear group GL_n(ℱ_q) and its applications in group theory.
  • Explore the relationships between cyclic groups and their automorphism groups in detail.
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Mathematicians, particularly those specializing in group theory, algebraists, and students studying advanced topics in abstract algebra.

jimmycricket
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Im calculating Aut(Aut(Aut(C_{73}))) and have got as far as Aut(Aut(Aut(C_{73})))\cong Aut(C_2\times C_2\times C_2) \times Aut(C_3)
I thought this was the answer but I have been told that Aut(C_2\times C_2\times C_2) \times Aut(C_3)\cong GL_3(\mathbb{F}_2)
Can someone explain this to me please.
 
From what I get, Aut(C_{73}) = U(73) = C_{72}. Aut(C_{72}) = U(72) = U(2^3) × U(3^2) = C_2 × C_2 × C_2 × C_2 × C_3 (since |U(3^2)| = phi(9) = 6 and only abelian group of order 6 is C_2 × C_3. So I think you're missing a factor of C_2 in your second Aut( ) expression.
 
Sorry I just realized that I made a mistake. U(2^3) = C_2 × C_2 so your expression is actually correct. My apologies.
 

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