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Old 2020-12-01, 21:37   #1
sweety439
 
Nov 2016

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Default 1021*2^n+1

Is 112 the only number n such that 1021*2^n+1 is prime?

Besides, if 47*2^a+1 and 383*2^b+1 are both primes, then a<b, is this true?
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Old 2020-12-02, 06:57   #2
Dylan14
 
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"Dylan"
Mar 2017

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Per the old rieselprime.de site, 1021*2^n+1 has been searched to 1.5 M, with n = 112 being the only prime.
It has been searched to n = 2903480 at PrimeGrid, with no prime found. No idea if there are more primes of this form.
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