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I've been trying to show that there are infinitely many primes in the form of $$ \frac {3^n - 1}{2}$$

Up until now I've tried a modified version Euclid's way of proving the infinity of primes but didn't find a solid answer. Do you have a particular way of approaching this problem? Any help will be appreciated.

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    $\begingroup$ Given that we don't know the same for $2^n-1$, it is unlikely that we know it for $(3^n-1)/2$, unless it is in the negative. We also don't know it for $(10^n-1)/9$ - the repunit primes. Basically, this is a hard sort of problem. $\endgroup$ – Thomas Andrews Nov 30 '16 at 19:44
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    $\begingroup$ Possible duplicate of Prime numbers of the form $(3^n-1)/2$ $\endgroup$ – CIJ Nov 30 '16 at 19:48
  • $\begingroup$ Not at all a duplicate. This is asking if there are infinite primes in the form. The other is to show some of the non-primes in the form. $\endgroup$ – fleablood Nov 30 '16 at 20:22

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