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Primes (Posted on 2003-09-09) Difficulty: 3 of 5
If x and (x² + 8) are both primes, then prove that (x³ +16) is also a prime.

See The Solution Submitted by Ravi Raja    
Rating: 4.2500 (12 votes)

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re(2): Second thought | Comment 4 of 9 |
(In reply to re: Second thought by SilverKnight)

More to the point... I think that if x is prime, x²+8 can not be prime for any x other than 3.

Therefore, the formula x³+16 is a red herring.... and the statement would be JUST as true if I wrote the third part as x³+14 or x³+2 or x²+2 (or any other formula based on x=3 that results in a prime number).

My head hurts.... anyone wanna corroborate this?
  Posted by SilverKnight on 2003-09-10 00:19:16

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