duplicate hunting cont., pt4

[Andrew Plewe]

squarefree). Thanks for your comments. With that, here are a few more for
straightforward duplicates:
	-Andrew Plewe-
From: Martin Fuller [mailto:martin_n_fuller at btinternet.com]
Sent: Tuesday, April 24, 2007 10:28 AM
To: seqfan at ext.jussieu.fr
Subject: Re: duplicate hunting cont., pt3
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From: "Ray Chandler" <rayjchandler at sbcglobal.net>
To: <seqfan at ext.jussieu.fr>
Cc: "'Andrew Plewe'" <aplewe at sbcglobal.net>
References: <427707.17686.qm at web86604.mail.ird.yahoo.com> <200704241942.l3OJgkFb094635 at shiva.jussieu.fr>
Subject: RE: duplicate hunting cont., pt4
Date: Tue, 24 Apr 2007 16:59:04 -0500
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> -----Original Message-----
> From: Andrew Plewe [mailto:aplewe at sbcglobal.net] 
> Sent: Tuesday, April 24, 2007 2:43 PM

> Sequences A087685 and A087749 match, but it appears that 
> A087749 is wrong.
> It is defined as "Primes n such that 6^n-5^n is composite." 
> Here are two
> examples of terms that are invalid:
> 
> A087749(1) = 2, 6^2 - 5^2 = 11, 11 is prime
> A087749(2) = 5, 6^5 - 5^5 = 4651, 4651 is prime
> 
> This is the Pari code included with the sequence:
> 
> apmb(a, b, n) = ( forprime(x=2, n, y=a^x-b^x; if(!ispseudoprime(y),
> print1(x", "); ) ) )
> 
> Running abpm(6,5,400) I get:
> 
> 3, 7, 17, 19, 29, 31, 37, 41, 43, 47, 53, 59, 67, 71, 73, 79, 
> 89, 97, 101,
> 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 
> 167, 173, 179,
> 181, 191,193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 
> 251, 257, 263,
> 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 
> 347, 349, 353,
> 359, 367, 373, 379, 383, 389, 397
> 
> Doing a lookup on the first fifteen or so terms of that 
> sequence returns no
> results. Can someone confirm that this is indeed the correct sequence?
> Thanks!
> 
> 	-Andrew Plewe-

I agree, the terms of A087749 are incorrect for the definition and should be replaced by the terms you calculated.  

A087685 is correct as is.  

Ray Chandler





Dear Friends, I accidentally deleted a few hundred "Comments"
on Apr 19 or 20.  I was able to recover all except about 75 
of these messages from backup files. The rest were all from
people whose email addresses I have, and I have written
to everyone concerned, asking them to re-send
the Comments (or the emails).

If you got an email message from me just now,
please send just the messages that I listed.
(You could just send me the confirmation email, for example)

I'm sorry about this.  I am running about 2 weeks behind
in processing "Comments".  Next week I will be traveling,
but I hope to get caught up by the middle of May.

Oh, there was one comment that I could not identify 
from the mail header (which is all that I got from the mail log),
namely:

 From oeis at research.att.com  Fri Apr 20 01:04:02 2007 Subject: COMMENT yousaf A637913724524516

(whereas a real comment has a header like this:
 From oeis at research.att.com  Thu Apr 19 16:59:49 2007 Subject: COMMENT Benoit Cloitre A061201
)

- I assume the one from "yousaf" is spam.

Neil