Largest 64 bit prime?

amcfarlane · 2004-12-26, 19:33

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

Xyzzy · 2004-12-26, 21:06

Xyzzy · 2004-12-26, 21:12

Code:

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

Xyzzy · 2004-12-26, 21:20

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

amcfarlane · 2004-12-26, 21:26

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

marc · 2004-12-26, 22:37

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

alpertron · 2004-12-26, 23:15

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

2004-12-26, 19:33	#1
amcfarlane Nov 2004 UK 38₁₀ Posts	Largest 64 bit prime? Can anyone tell me please what the largest prime number is that will fit into a 64-bit unsigned variable?

2004-12-26, 21:20	#4
Xyzzy Aug 2002 7×17×73 Posts	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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2004-12-26, 21:06	#2
Xyzzy Aug 2002 21EF₁₆ Posts	Sounds like a homework problem! http://www.utm.edu/research/primes/l...mall/0bit.html

2004-12-26, 22:37	#6
marc Jun 2004 UK 139 Posts	Might want to set your while loop to != 0 or even just something like while [ " " ] and there's the obvious += 2 time saver.

2004-12-26, 23:15	#7
alpertron Aug 2002 Buenos Aires, Argentina 3×7×73 Posts	Just write b(2^64) in my factoring applet.