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Math Help - primes

  1. #1
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    primes

    Let n>1. If (n^2)+2 is a prime show that 3 divides n.

    Can anyone help me start this exercise? Thank you
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  2. #2
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    Quote Originally Posted by AlexHall View Post
    Let n>1. If (n^2)+2 is a prime show that 3 divides n.
    Try proving the contrapositive. If 3 does not divide n then n must be of the form 3k+1 or 3k+2. Show that in both cases (n^2)+2 is then a multiple of 3.
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