Show that 2k+1 cannot be a prime unless k is a power of 2. [Hint: Find a (polynomial) factor of Xp+1 for every odd prime p.]
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Setting $\displaystyle k=6$ we find that $\displaystyle 2k+1= 13$ is prime... but 6 is not a power of 2 !... Kind regards $\displaystyle \chi$ $\displaystyle \sigma$
Originally Posted by NikoBellic Show that 2k+1 cannot be a prime unless k is a power of 2. [Hint: Find a (polynomial) factor of Xp+1 for every odd prime p.] I suspect you mean $\displaystyle 2^k+ 1$.
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Originally Posted by HallsofIvy I suspect you mean $\displaystyle 2^k+ 1$. Yeah, the formatting got lost for some reason.
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