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Old 2008-05-23, 13:36   #1
Housemouse's Avatar
Feb 2008

25 Posts
Default 10^N+1

For all N>2, is 10^N+1 always composite?
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Old 2008-05-23, 13:39   #2
wpolly's Avatar
Sep 2002
Vienna, Austria

DB16 Posts
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Old 2008-05-23, 15:27   #3
Just call me Henry
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Sep 2007
Cambridge (GMT/BST)

2×41×71 Posts
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Old 2008-05-28, 00:20   #4
geoff's Avatar
Mar 2003
New Zealand

100100001012 Posts

10^2^23+1 = 10^8388608+1 is the smallest candidate that hasn't yet been shown to be composite. It would take about 89 days to do a PRP test on this number using a 2.66GHz Core 2. Some more trial factoring would probably be worthwhile before starting the PRP test.
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