# 257

This number is a prime.

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257 is the largest known prime of the form N^N+1. Note that
if N^N+1 (for N>1) is a prime then it must be of the
form 2^2^(2^m+m)+1 (m>=0). So according to the Fermat
number factoring status, the next prime of the form N^N+1
(if it exists) is may be 2^2^70+1 and will have more than
8*10^20 digits (!). [Antonious]
Submitted: 2018-12-20 06:04:32; Last Modified: 2018-12-20 08:21:32.

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