A seqfan forum...

[Tanya Khovanova]

sites.  If this will happen it will hopefully make those prime
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To: seqfan <seqfan at ext.jussieu.fr>
From: Gordon Royle <gordon at csse.uwa.edu.au>
Subject: A seqfan problem - refocus
Date: Fri, 12 Jan 2007 14:19:02 +0900
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seqfan community and that we should be able to find a solution.
submissions and postings are made but that people who do not want  
solutions that will stop people POSTING, there certainly ARE  
solve or in any way address the original problem. Simply being  
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Date: Fri, 12 Jan 2007 00:48:20 -0500 (EST)
From: Emeric Deutsch <deutsch at duke.poly.edu>
To: David Wilson <davidwwilson at comcast.net>
cc: Sequence Fans <seqfan at ext.jussieu.fr>
Subject: Re: Adieu (fwd)
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David,
Sorry to contradict you. Firstly, do not mix seqfan
mail with OEIS; they are not inseparable. Working
for OEIS is not a losing battle. It is extremely
valuable.
For example, OEIS helped me a lot in my research.
I will mention only two instances.
1. It is well-known that the Catalan number C_n is
odd only for n=1, 3, 7, 15, 31, ... .
It was obvious to look into the parity of the
Motzkin numbers M_n. Thanks to Maple, it was no
problem to find the first few hundred values of
n when M_n is odd. But they haven't betrayed any
regularity. Thanks to OEIS, it turned out that
they form a sequence related to the Thue-Morse
sequence. This led to a conjecture, followed by
a proof. It resulted in a paper (with Bruce Sagan),
published in J. of Number Theory.
2. Recently, I have contributed sequence A125182,
the triangle of T(n,k)=number of permutations p of
{1,2,...,n} such that the set {p(i)-i,i=1,2,...,n}
has exactly k elements. 
Column 2 of this triangle is 1,2,4,4,8,6,11,10,... .
I assume very few people would recognize this
series. But OEIS told me that this is the sequence of
the "sum of divisors of n - number of divisors of n". 
Max Alekseyev has proved it and it will appear shortly
as a problem in the Monthly.

So, please continue to work for OEIS, for the benefit
of all of us.
Best regards and Happy 2007,
Emeric



On Thu, 11 Jan 2007, David Wilson wrote:

We lost JHC a while ago, now Antti and RKG.  I remember
a few others who have unsubscribed. And I'm sure there
are many, like myself, who page through their seqfan mail
these days with barely a glance. We have lost those people
too, quietly.
But I think the worst part of it is, I have lost much of
my enthusiasm for the OEIS. When I first started working
on it, I used to get a great deal of pleasure out of
tracking down and fixing errors and extending sequences
and such, thinking that my work to some extent raised the
overall quality of the OEIS. But now I feel like its a
losing battle.