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25392RE: Re: [PrimeNumbers] Re: Yet another factoring puzzle

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  • djbroadhurst
    Sep 27, 2013
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       ---In primenumbers@yahoogroups.com, <thefatphil@...> wrote:

       

      > You only chose that target after
      > the arrow had landed, I'm sure.

       

      It happened thus:

       

      1) I determined to factorize F(n)=((n^2-9)/4)^2-5 for
      n <= 300, completely. As later shown in "factordb", I succeeded.

       

      2) Meanwhile I ran OpenPFGW on n in [301,600], hoping for a
      quick outlier and found none.

       

      3) I estimated the probability of an easily discoverable
      completely factorization for n>600 and found it to be small.

       

      4) Recalling how I had once been caught out before by
      a "probably no more" heuristic, I set a lone process running on
      n in [601, 10000]  so as not to be caught out again by Jens.

       

      5) When I later looked  and pfgw.log, it had found a hit at
      n=608.

       

      So yes, Phil, you are quite correct that the puzzle was set
      after this finding. However the heuristic that I gave was
      made prior to my discovery, else I would not have said that
      I was surprised.

       

      The point that you are making (I think) is that I do such 
      expsriments often and only notice when the result is unexpected.
      I don't tell folk about all the boring times when a negative
      heuristic is borne out by a null result. That is the selection

      effect.

       

      David (guilty of not boring folk with what is routine)

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