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Old 2009-09-07, 13:07   #9
Brian-E's Avatar
Jul 2007
The Netherlands

326610 Posts

Originally Posted by Mini-Geek View Post
I'm 99% sure that triple checks are very close to being totally useless. (unless for some other purpose...definitely not useful in the same way that double checks are useful) I think the odds of Prime95 having a bug that would produce matching residues (which is very small) is better than the chance that two 64-bit residues just happened to match when they're both wrong, so a third check wouldn't be useful.
The extra LL results (triple-, quadruple-, etc. checks) in small exponents is likely due to people playing around. (one time, I went through a list of small-ish primes and re-discovered the first couple dozen or so Mersenne primes, just for fun if I had submitted my results to PrimeNet, they'd appear as more matching LL results on those small numbers)
Yes I agree with you really. An example of some other purpose was hinted by garo:

Originally Posted by garo View Post
Also, occasional triple-checks are useful for GIMPS as they provide error rate data that can be useful.
but for purposes of purely being certain that no other Mersenne numbers in the given range are prime, the only serious use of triple checking would seem to be with completely different client software to allow for the possibility of a bug as you mention, and that is largely handled by the random offset at the start of a LL test, we would hope.

Can anyone tell us why so much of the lower end of the exponents have been triple checked? Is it just people having fun, is it for the error rate data, or are there other concrete reasons too?
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