(pp-1)/2 is prime: {27, 2187,...}
Dean Hickerson
dean at math.ucdavis.edu
Tue Oct 15 05:43:32 CEST 2002
Robert G. Wilson v" <rgwv at kspaint.com> wrote:
> All that I found < 10^7 are 27, 2187 and 159323.
That last one should be 1594323.
The point of my message was that you don't have to check all perfect powers,
only those of the form 3^p with p prime. The first 12 perfect powers pp
such that (pp-1)/2 is prime are:
3^3 = 27,
3^7 = 2187,
3^13 = 1594323,
3^71 = 7509466514979724803946715958257547,
3^103, 3^541, 3^1091, 3^1367, 3^1627, 3^4177, 3^9011, 3^9551
Dean Hickerson
dean at math.ucdavis.edu
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