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Old 2013-09-17, 18:48   #2
Batalov's Avatar
Mar 2008

3·31·97 Posts

Only Generalized Fermat numbers (in base 10 in this case), can be prime:
10N+1, where N=2n.

And even these are very rarely prime. It is conjectured that there's only a finite number of them.

You can see the start of the series here and here.
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