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Math Help - Coprime Test

  1. #1
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    Coprime Test

    I read two numbers a and b are coprime if b^{a - 1} = 1 (mod a). Is it me or does this test not hold when a = 6 and b = 5, which are coprime?

    5^{6 - 1} = 1 (mod 6)
    5^5 = 1 (mod 6)
    3125 = 1 (mod 6)

    3125 mod 6 is 5, which does not equal 1, so the test fails. Is it me or the test?
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