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Homework Help: Modulo arithmetic - fact?

  1. Jan 1, 2013 #1
    Is it true that if [itex]A \equiv B \mod{\varphi(N)}[/itex] where [itex]\varphi (N)[/itex] is Euler's totient function then [itex]a^A \equiv a^B \mod{N}[/itex]?

    I'm not after a proof or anything but I didn't do a number theory course and it seems that this fact is used in many questions I'm currently doing.
  2. jcsd
  3. Jan 1, 2013 #2


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    You need to assume gcd(a,N)=1 as well.
  4. Jan 1, 2013 #3
    The more popular format is

    [itex]a^{\varphi(n)}\equiv 1 (mod \;n)[/itex] where [itex] gcd(a,n)=1[/itex]
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