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Old 2004-12-26, 19:33   #1
amcfarlane
 
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Default Largest 64 bit prime?

Can anyone tell me please what the largest prime number is that will fit into a 64-bit unsigned variable?
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Old 2004-12-26, 21:06   #2
Xyzzy
 
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Sounds like a homework problem!

http://www.utm.edu/research/primes/l...mall/0bit.html

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Old 2004-12-26, 21:12   #3
Xyzzy
 
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Code:
mv@k8:~$ echo '2^64-59' | bc | factor
18446744073709551557: 18446744073709551557
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Old 2004-12-26, 21:20   #4
Xyzzy
 
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Had I not cheated with that link, I would have done this:

Code:
#!/bin/sh
counter=1
while [ $counter != 1 ]
do
        echo '2^64-'$counter | bc | factor
(( counter += 1 ))
done
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Old 2004-12-26, 21:26   #5
amcfarlane
 
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That's very clever ! -- Thanks...
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Old 2004-12-26, 22:37   #6
marc
 
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Might want to set your while loop to != 0 or even just something like while [ " " ] and there's the obvious += 2 time saver.
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Old 2004-12-26, 23:15   #7
alpertron
 
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Just write b(2^64) in my factoring applet.
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