Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Finding Aut(Aut(Aut(C_73)))

  1. Jan 22, 2015 #1
    Im calculating [itex]Aut(Aut(Aut(C_{73})))[/itex] and have got as far as [itex]Aut(Aut(Aut(C_{73})))\cong Aut(C_2\times C_2\times C_2) \times Aut(C_3)[/itex]
    I thought this was the answer but I have been told that [itex]Aut(C_2\times C_2\times C_2) \times Aut(C_3)\cong GL_3(\mathbb{F}_2)[/itex]
    Can someone explain this to me please.
  2. jcsd
  3. Jan 27, 2015 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
  4. Feb 5, 2015 #3
    From what I get, [itex]Aut(C_{73}) = U(73) = C_{72}[/itex]. [itex]Aut(C_{72}) = U(72) = U(2^3) × U(3^2) = C_2 × C_2 × C_2 × C_2 × C_3 [/itex] (since [itex]|U(3^2)| = phi(9) = 6[/itex] and only abelian group of order 6 is [itex]C_2 × C_3[/itex]. So I think you're missing a factor of [itex]C_2[/itex] in your second Aut( ) expression.
  5. Feb 6, 2015 #4
    Sorry I just realized that I made a mistake. [itex] U(2^3) = C_2 × C_2 [/itex] so your expression is actually correct. My apologies.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook