Finding the Least Residue of 3^215 (mod 65537)

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The discussion focuses on computing the least residue of \(3^{215} \mod 65537\), where 65537 is identified as a Fermat's prime. Participants reference Euler's theorem, Fermat's little theorem, and Wilson's theorem in their attempts to solve the problem. A key clarification is made regarding the exponent, where \(3^{215}\) is corrected to \(3^{2^{15}}\), leading to the conclusion that \(3^{2^{15}} \equiv -1 \mod 65537\).

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Compute the least residue of 3^215 (mod 65537) (65537 is prime).

I've tried to use Euler's theorem, Fermat's little theorem and Wilson's theorem, but nothing seems to work, please help.
 
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crypt50 said:
Compute the least residue of 3^215 (mod 65537) (65537 is prime).

I've tried to use Euler's theorem, Fermat's little theorem and Wilson's theorem, but nothing seems to work, please help.

The number 65537 is not a 'whatever prime', it is a Fermat's prime because is in the form $\displaystyle F_{n}= 2^{2^{n}}+1$. For a Fermat's prime the following holds...

$\displaystyle 3^{\frac{F_{n}-1}{2}} = -1\ \text{mod}\ F_{n}\ (1)$

For n=4 the (1) becomes...

$\displaystyle 3^{2^{15}} = -1\ \text{mod}\ 65537\ (2)$

In your post is written $\displaystyle 3^{215}$ and not $\displaystyle 3^{2^{15}}$... the question is: are You sure to have written correctly?... Kind regards $\chi$ $\sigma$
 
Last edited:
Thanks, a lot I didn't realize it was 3^2^15. Thanks for calling my attention to it.
 

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