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The purpose of sieving is to reduce the number of candidates that have to be primality checked by finding factors for those candidates. A factor is a number which divides a candidate.
So if you found 4 factors in one PPS sieve WU, you showed that 4 of the candidates in the sieve file are composite. They will be deleted from the sieve file and when it's time for the primality tests, they will not be tested because we already know they are not prime.
What you did is rather the "opposite" of finding a prime. When a new range of numbers gets worked on, sieving is much more efficient than primality testing E.g. one primality test might last 8 minutes, but 8 minutes of sieving might find 3 factors. So sieving reduces the number of remaining candidates faster than primality testing. As more and more candidates are removed, sieving finds factors less quickly, until it's less effective than testing every remaining candidate.This is the time to switch methods. But you'll never find a prime via sieving.
I'm not running a sieve right now so I can't copy a line, but you'll find something which looks like this in the factor file:
152374867 | 2756*2^487533
That means that 152374867 is a factor of 2756*2^487533, so we know that 2756*2^487533 is not prime.
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There are only 10 kinds of people - those who understand binary and those who don't
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