Without doing any calculations in Aut(Z_20), determine how many elements of Aut(Z_20) have order 4. How many have order 2?
The only way I can think to do this problem is to apply Thm. 6.5 on page 131 which says that Aut(A_20) is isomorphic to U(20) and thus rind the orders of each element. However, that is applying calculations so I am confused.
--Robertsr 22:53, 7 October 2008 (UTC)
