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Numbers n such that 8^n + 7 is prime.
1

%I #18 Jul 23 2017 21:50:40

%S 2,6,10,26,42,58,68,196,266,602,1170,1288,1290,2990,4110,6292,7446,

%T 36928,57490,65478,78570,188832

%N Numbers n such that 8^n + 7 is prime.

%C All terms are equal to 1/3 of the multiples of 3 in A057195.

%C Naturally these numbers are even because (9-1)^(2n+1)+7 is divisible by 3. - _Bruno Berselli_, Oct 03 2012

%t Select[Range[10000], PrimeQ[8^# + 7] &]

%o (PARI) is(n)=ispseudoprime(8^n+7) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A057195, A217354, A217355.

%Y Cf. A144360 (associated primes).

%K nonn

%O 1,1

%A _Vincenzo Librandi_, Oct 02 2012

%E a(18)-a(22) from A057195 by _Robert Price_, Jul 23 2017