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 2011-11-26, 01:55 #1 davieddy     "Lucan" Dec 2006 England 647410 Posts Never a dull moment around here One minute I'm discussing TF to 72, and the next I am failing to get UncWilly to grasp that if for some bizarre reason you want to trawl the exponents <1 Billion for factors, it would be better to work downwards. David
2011-11-26, 02:34   #2
science_man_88

"Forget I exist"
Jul 2009
Dumbassville

26·131 Posts

Quote:
 Originally Posted by davieddy if for some bizarre reason you want to trawl the exponents <1 Billion for factors, it would be better to work downwards.
really, on second thought I don't see it as bizarre because 2*k*p+1 if k= composite such that it breaks into 2 primes r,s smaller than p such that 2*k*p+1 is lower than 2^r-1 or 2^s-1 or both. if k is prime switch p and k you've now got a impossible factor of 2^k-1 if 2*k*p+1 is less than 2^k-1. the bizarre part for me would be the likelihood of such happening.

edit: k could also be composite * prime and be composite.

Last fiddled with by science_man_88 on 2011-11-26 at 02:35

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