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November 24th, 2017, 10:06 AM   #1
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A question about primes

Hi, I have a question about primes here. I was just wondering if any whole number plus one half could be used to find primes. for example, 1.5,2.5,3.5...
The way I see it, you shouldn't round up or down from these numbers and I was wondering if anybody could establish for me the logic behind rounding up, say, from 1.5 to 2.
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November 24th, 2017, 10:16 AM   #2
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Once you have a candidate how would you test it for primality?
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November 24th, 2017, 06:59 PM   #3
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Quote:
Originally Posted by Pegleggedninja View Post
Hi, I have a question about primes here. I was just wondering if any whole number plus one half could be used to find primes. for example, 1.5,2.5,3.5...
The way I see it, you shouldn't round up or down from these numbers and I was wondering if anybody could establish for me the logic behind rounding up, say, from 1.5 to 2.
What in the world does this have to do with prime numbers? When thinking about prime numbers, we are only dealing with whole numbers.

If you round up 3.5 you get 4, which is NOT prime.

Last edited by skipjack; November 24th, 2017 at 09:44 PM.
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November 24th, 2017, 10:33 PM   #4
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That wouldn't stop one from asking whether, for some prime $p$ (such as 131), $q = \sqrt{4p-163}$ is an integer, and $p + q + 1$ another prime.
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