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Old 2007-01-10, 12:32   #2
thommy
 
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Dec 2006

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Quote:
Originally Posted by Citrix View Post
What is the lowest base=b for k=2 such that 2*b^n+1 is never prime?

b=4, as 2*1^1+1 and 2*2^1+1 and 2*3^1+1 are prime
For all n : 2*4^n+1=2*1^n+1=2*1+1=3=0 (mod 3), so every number divisible by 3.
Those questions seem not that interesting.
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