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Topic: Three forever (Read 579 times) |
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Benny
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Three forever
« on: Aug 23rd, 2011, 4:46pm » |
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On perplexus I posted an answer to
Choose a prime number greater than 3.
Multiply it by itself and add 14.
Divide by 12 and write down the remainder.
It will always be 3.
WHY?
I received no feedback. Is my answer wrong? If so, why?
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Grimbal
wu::riddles Moderator
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Re: Three forever
« Reply #1 on: Aug 24th, 2011, 2:20am » |
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A prime p>3 is odd and not divisible by 3.
Modulo 12 p can only be 1, 5, 7, 11.
The remainder modulo 12 of p*p+14 depends only on the class of p modulo 12. So if the formula works for these 4 cases, it works for all odd numbers not divisible by 3.
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pex
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Re: Three forever
« Reply #2 on: Aug 24th, 2011, 3:21am » |
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on Aug 23rd, 2011, 4:46pm, BenVitale wrote:| I received no feedback. Is my answer wrong? If so, why? |
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No, your answer seems perfectly valid. The reason you received no feedback is probably that you were the fifth person to post basically the same solution, in a thread that had been dead for almost a year.
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