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Old 2005-08-18, 09:49   #1
Aug 2005

22 Posts
Lightbulb Factor me this

e.g Can someone tell me if the following number is prime (or how do I find out for myself):

(2 ^ 65536) + 1

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Old 2005-08-18, 10:58   #2
jinydu's Avatar
Dec 2003
Hopefully Near M48

2·3·293 Posts

This question was already posted in the Soap Opera
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Old 2005-08-18, 16:00   #3
akruppa's Avatar
Aug 2002

9A316 Posts

...but better fits into the Factoring forum.
This is the 16-th Fermat number. The small Fermat numbers have received great factoring efforts already, discovering new factors will be very hard. Use Google or the Forum search to find out more.

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Old 2005-08-18, 20:33   #4
sean's Avatar
Aug 2004
New Zealand

2×3×37 Posts

No it is not prime. We can tell you this without exhibiting a factor.
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Old 2005-08-21, 11:19   #5
ATH's Avatar
Dec 2003

3,079 Posts

As you can se under F16 there is 2 known factors 825753601 and 188981757975021318420037633 but there is still a 19694 digit number left that is composite.
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