Quote:
Originally Posted by a1call
The Mersenne part has been known since 1775 as proven in this link first shown to me by sm:
https://primes.utm.edu/notes/proofs/MerDiv2.html
It is of practical use in proving factors of Mersenne numbers with prime exponents prime.
23 is guaranteed to be prime because it divides M11 and 23= 2*11+1

341 divides M170 and 341=2*170+1, but 341 is not prime