View Single Post
Old 2013-09-17, 18:48   #2
Batalov
 
Batalov's Avatar
 
"Serge"
Mar 2008
Phi(3,3^1118781+1)/3

22·3·7·107 Posts
Default

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.
Batalov is offline   Reply With Quote