About this project

Come one, come all!

Come one, come all! This is a very exciting project where we hope to find many top-5000 primes in a short period of time.

With this project, the primary focus will be to do Riesel prime tests of the form k · 2^n - 1 for 300 < k <= 1001 that have not been reserved by others or are not being actively worked on.
k < 300 and 1001 < k < 1400 are already being searched by other projects or individuals.

This forum is to coordinate and extend prime searching at Michael Hartley's originally well-designed 'Prime Search' site that has now gone defunct. It is believed that the prime-searching community originally largely ignored this testing range because there was previously no forum to coordinate sieving and searching. This forum has changed that and has brought testing up to where it should be.

Sieve files have been prepared in advance for all n-ranges. We are running team drives for all ranges as follows:

  • PRPnet automated testing for 5 k's in k = 300 - 310 and n > 4M.
  • PRPnet automated testing for 45 k's in k = 310 - 400 and n > 3M.
  • PRPnet automated testing and manual reservations for k = 400 - 1001 and n > 2M.

  • Subprojects will include:
  • Testing of other k-values outside the original scope of the project that are significantly behind their neighbors as to how far they have been searched. If necessary, coordination with existing reservations at other sites will be done ahead of time. This is the crux of the entire project.

  • The main two goals of the project relate to all k <= 1001 and are as follows:
  • All k's should be fully tested to the top-5000 range at all times.
  • All k's should have their non-top-5000 ranges tested.

  • Please see other threads in the forum for questions about searching and software.

    For information and downloads for the manual version of LLR or sr(n)sieve, please see the software/instructions/questions thread.
    For information on running PRPnet clients on our servers, please refer to our PRPnet thread.

    If you would like to be automatically notified by Email of primes found on PRPnet servers, please see automatic prime notification in this thread.

    Thanks and come join us for the fun at No Prime Left Behind!

    Gary Barnes

    Background Information:

    This project searches for Riesel primes of the form k · 2 n - 1 with odd k and 300 < k <= 1001 and n > 260000 not reserved by others with highly presieved ranges.

    This project was founded with the intention of managing and continuing the PrimeSearch project in a more interesting manner for everyone.

    There are efforts for both lone searchers and for coordinated team efforts, which results in a higher precision of prime reporting.

    For more information visit the forum using the Community link on the menu.


    NPLB has been operational since: 2008-01-10

    PrimeSearch was set up by Michael Hartley in 2001 for the search of prime numbers of the form k · 2 n - 1 with 255 <= k <= 1001 and 16000 < n < 600000. The range for k < 255 was added in 2007.

    Many of the reasons for creating the project related to the following problems at PrimeSearch:

  • Every reserved range (in n=20k chunks) had to be sieved by the contributor himself.
  • PrimeSearch only collected primes without any test results so there were many missing or incorrect primes.
  • There was no forum helping the contributors with problems or questions and coordinating their search.
  • There were 'contributors' filling in primes that were obtained from other sites without doing any actual testing.

  • In 2007, Gary Barnes decided to correct all of these issues and began to sieve 400 < k <= 1001 from n = 260000 to 600000.
    That same year, Karsten Bonath began to sieve and test a range of 100 k's with k > 300.
    So in just a matter of time NPLB was born.