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

David C Terr David_C_Terr at raytheon.com
Mon Mar 14 21:22:36 CET 2005

```Sorry, my mistake - replace 78557 with 509203, the smallest known Riesel

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
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.

--
Don Reble  djr at nk.ca

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