Largest 64 bit prime?

[amcfarlane]

Can anyone tell me please what the largest prime number is that will fit into a 64-bit unsigned variable?

[Xyzzy]

Sounds like a homework problem!

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

[Xyzzy]

mv@k8:~$ echo '2^64-59' | bc | factor
18446744073709551557: 18446744073709551557

[Xyzzy]

Had I not cheated with that link, I would have done this:

#!/bin/sh
counter=1
while [ $counter != 1 ]
do
        echo '2^64-'$counter | bc | factor
(( counter += 1 ))
done

[amcfarlane]

That's very clever ! -- Thanks...

[marc]

Might want to set your while loop to != 0 or even just something like while [ " " ] and there's the obvious += 2 time saver.

[alpertron]

Just write b(2^64) in my factoring applet.