[seqfan] Re: A139414

Ray Chandler rayjchandler at sbcglobal.net
Tue Jan 27 19:24:32 CET 2009

>  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
A third option is to just drop terms where there is no prime, but that messes up the index.

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