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16009Re: [PrimeNumbers] Help please... user or pgm bug with NewPGen 2.82 on AMD & P4

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  • Jens Kruse Andersen
    Jan 30, 2005
      Chuck wrote:

      > I sieved, for 24 hours as is (I am told) the norm using NPG.

      The norm for any sieve is to sieve until the removal rate is similar to the
      prp/test time (which may be a complicated issue for a fixed k sieve).

      > I did the most rudimentary test: k.b^n-1
      > using: k=7, b=2, 2<=n<=65536
      > @ P=1G, K=7,N=29 was in the NPG as the lowest file.
      > @ P=5G, it was gone... as were MANY of valid K N
      > (which would yield prime) values.

      The prime 7*2^29-1 = 3758096383 is between 1G and 5G (G = 10^9).
      As Jim also thinks, NewPGen probably removed it when the prime was found as
      factor of itself.
      Some of my sieves knowingly do the same.
      Users and programmers can argue about whether something is a bug or feature.

      If NewPGen also removes some known primes above the sieve limit:
      Can you give examples?
      Have you checked "Verify results" ?

      The help says:
      If "Verify results" is checked, NewPGen will do a careful check to make sure
      that the prime actually does divide the number that it thinks it does. This
      will make NewPGen very slightly slower, but it is recommended that it is
      always checked, particularly as p gets large (where the scope for programming
      errors increases)

      If you check "Log the numbers removed" in the Options menu then NewPGen will
      write which prime removes a candidate, but only for primes above 2^32.

      Jens Kruse Andersen
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