[seqfan] Re: A139414

[David Wilson]

This is a sequence I would personally vote off the island. It looks 
contrived, and nothing in the sequence gives me the slightest reason to 
care about it. Is there some reason I should be interested?


Harry J. Smith wrote:
> I vote for defining a(79)=0.
>
> 76 13381
> 77 14087
> 78 14561
> 79 0
> 80 15541
> 81 15791
> 82 16553
>
> I will add some comments to the sequence A139414 and submit a b-file.
>
> -Harry
>
>
>   
>> -----Original Message-----
>> From: seqfan-bounces at list.seqfan.eu [mailto:seqfan-bounces at list.seqfan.eu]
>>     
> On
>   
>> Behalf Of Ray Chandler
>> Sent: Tuesday, January 27, 2009 10:25 AM
>> To: 'Sequence Fanatics Discussion list'
>> Subject: [seqfan] Re: A139414
>>
>>     
>>>  i tried to understand A139414
>>>  (and then submit comment etc.) but failed, see:
>>> http://zak08.livejournal.com/5346.html
>>>
>>> Hope someone with better English/math
>>> (better than Roger?! ...i doubt...)
>>> may wish to submit a proper comment/editing,
>>>
>>> thx, zak
>>>       
>> Looking at the code included with the sequence, the polynomials are tested
>>     
> in a cycle
>   
>> beginning with a[1 + Mod[x,4]],
>> i.e. when x==0 mod 4, they are tested in order a1,a2,a3,a4; when x==1 mod
>>     
> 4, they are
>   
>> tested in the order a2,a3,a4,a1,
>> etc.  That answers the question already posted in comments about which
>>     
> prime to
>   
>> choose if there are multiples.
>>
>> The second question regarding what to do if none of the polynomials
>>     
> produces a
>   
>> prime, cannot be answered so easily.
>> Since the examples stop with x=78 and the first occurrence of no prime
>>     
> occurs at x=79
>   
>> , it is not clear what the
>> author's intent was.
>> The sequence could simply stop at that point ("fin") or we could add "or
>>     
> zero if no
>   
>> prime exists" to definition and
>> continue.
>> A third option is to just drop terms where there is no prime, but that
>>     
> messes up the
>   
>> index.
>> Ray
>>
>>
>>
>>
>>
>>
>>
>>
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>
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