n => 2n+1 to get prime: seed = 73

[David C Terr]

Sorry, my mistake - replace 78557 with 509203, the smallest known Riesel 
number. Here's a link:

http://mathworld.wolfram.com/RieselNumber.html

Dave







זקיר סעידוב - ד\"ר/Zakir Seidov Ph.D. <zakirs at yosh.ac.il>
03/14/2005 11:42 AM

 
        To:     David C Terr <David_C_Terr at raytheon.com>, Don Reble <djr at nk.ca>
        cc:     זקיר סעידוב - ד\"ר/Zakir Seidov Ph.D. <zakirs at yosh.ac.il>
        Subject:        RE: n => 2n+1 to get prime:  seed = 73

David,
thank your very much for this 78557
(can you give any link, please?).
As to seed=36, the rule n => 2n+1 gives prime at the first step,
so no need to look further!
Zak
-----Original Message----- 
From: David C Terr [mailto:David_C_Terr at raytheon.com] 
Sent: Mon 3/14/2005 7:45 PM 
To: Don Reble 
Cc: זקיר סעידוב - ד"ר/Zakir Seidov Ph.D.; Seqfan 
Subject: Re: n => 2n+1 to get prime: seed = 73


This process should lead to a prime unless n is a Sierpinski number, the 
smallest known being 78557. For the example below, why not start with 36? 

Dave 





Don Reble <djr at nk.ca> 
03/11/2005 05:47 AM 
        
        To:        zakirs at yosh.ac.il, Seqfan <seqfan at ext.jussieu.fr> 
        cc:         
        Subject:        Re: n => 2n+1 to get prime:  seed = 73


> Dear Seqfans,
> The operation n => 2n+1 quickly gives primes for most "seed" values of 
n.
> But for some seeds, the transformed numbers keep being composite.
> The first "tough" number is n=73.
> Can the n =>2n+1 transformation, in this particular case,
>  lead to prime number (and when?),

Starting from 73, the 2552nd number (74 * 2^2552 - 1) is prime. It's a
771-digit number which begins and ends 12525...16703.

See also A040081.

-- 
Don Reble  djr at nk.ca





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