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Old 2017-04-20, 17:17   #52
Batalov
 
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Mar 2008
Phi(4,2^7658614+1)/2

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Quote:
Originally Posted by Dr Sardonicus View Post
...FWIW, I checked 10^n + 7 up to the limit n = 2000, and found pseudoprimes for the exponents

n = 1, 2, 4, 8, 9, 24, 60, 110, 134, 222, 412, 700, 999, and 1383.

I don't see any obvious pattern. ...
10^n+7 is in Kamada's collection. Many more PRPs are known for it, as well as many factorizations for n<=300
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