[seqfan] Re: both p -/+ 2 is prime power
W. Edwin Clark
wclark at mail.usf.edu
Sat Oct 17 14:01:19 CEST 2015
On Sat, Oct 17, 2015 at 4:39 AM, Robert Gerbicz <robert.gerbicz at gmail.com>
wrote:
> 2015-10-17 10:12 GMT+02:00 W. Edwin Clark <wclark at mail.usf.edu>:
>
> > If p = 7 then p+2 = 9 is not prime.
> >
>
> Wrong, he needs prime power, not prime.
>
Oops. I misread.
> The next two terms: 450283905890997361,36472996377170786401
> and it is likely that there is no more terms: if p>3 then p-2 or p+2 is
> divisible by 3, but as that is a prime power it should be in the form of
> 3^k. So we need: 3^k+2 is prime and 3^k+4 is prime power, or 3^k-2 is prime
> and 3^k-4 is prime power.
>
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