BOINC@AUSTRALIA FORUM

Active BOINC projects => PRIMEGRID@HOME => Topic started by: Dingo on December 09, 2019, 08:27:37 PM

Title: Manual Sieving.
Post by: Dingo on December 09, 2019, 08:27:37 PM
I have been doing some manual sieving and thought that it found the numbers that would most likely be primes.  Well I asked the question on the Primegrid forum and the Project Scientist informed me that was absolutely wrong as the sieveinf ound numbers that were not Primes.

Quote
My Question:

What is the meaning of the two numbers of Manual Sieving. Is Sieving finding numbers that might be Prime ?

959815134871698800641 | 709500654^2097152+1
959815195922830196737 | 802617394^2097152+1

A layman's answer if possible.

Ravi Fernando, Project scientist, gave me the following answer.

QuoteIt's the opposite: sieving identifies numbers that definitely aren't prime, because they have nontrivial factors. The vertical bar symbol "|" means "divides", or in normal English "is a factor of". So what you wrote says that the two GFN-21 numbers on the right, each with over 18 million digits, are multiples of the 21-digit numbers on the left, and in particular can't be prime. This saves us the work of testing the 18-million-digit numbers further.

Related thread: here. (https://www.primegrid.com/forum_thread.php?id=8728&nowrap=true#131594)
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