Friday, January 26, 2024

A million-digit Leyland prime (end of 2nd run)

My second run of 59754 Leyland-prime candidates was started on 27 April 2023 and resulted in my finding three PRPs (the first column is the number of decimal digits):

1000905  (197180,119151)  Aug 2023
1000910  (191319,170462)  Jul 2023
1000999  (194968,136197)  Dec 2023

I blogged my first run here. As I did last year, I have documented my primality-test output. Search for PRP therein to situate the three primes. I have improved my average evaluation time per test from 9.45 hours to 5.55 hours but I was wrong in predicting that "I might be able to shave a couple of months off the total time required". It still took nine months. Some of that expected time saving was eaten up by the additional 218 tests. Some more, perhaps, by down-time as I have had a few battery-back-up units shutting themselves off, presumably because they are getting old. The remainder of the unmaterialized time saving would be an early start on a third search which began on some of my machines back on December 11.

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