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Disprove: If p is prime, then (2^p)-1 is also prime. Help?

Guest Feb 21, 2017
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 #1
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Disprove: If p is prime, then (2^p)-1 is also prime. Help?

 

Well that was easy :)

I only need to find one time where 2^p-1 is not prime and then it will be disproven!

 

I just tried them one at a time and found

 

2^11 = 2048

factor(3047) = 11*277                 I used the web2.0calculator for this :)

 

so

2^11-1 = 11*277 so it is not prime

 

Hence

If p is prime, then (2^p)-1 is also prime, has been disproven.  :)

Melody  Feb 21, 2017
 #2
avatar+10614 
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I think that should be factor (2047) factor (2047) = 23*89       Which also gives a viable answer to disprove the hypothesis.

ElectricPavlov  Feb 22, 2017

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