[seqfan] Re: both p -/+ 2 is prime power
Robert Gerbicz
robert.gerbicz at gmail.com
Sat Oct 17 10:39:55 CEST 2015
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.
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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