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Numbers k such that 6^k - 7 is prime.
4

%I #28 Oct 27 2024 13:02:55

%S 2,4,6,8,9,10,15,20,46,49,61,98,110,144,266,344,978,1692,1880,1924,

%T 3142,3220,4209,5708,7064,13465,13858,19474,22666,26807

%N Numbers k such that 6^k - 7 is prime.

%C a(31) > 50000. - _Michael S. Branicky_, Oct 27 2024

%t Select[Range[10000], PrimeQ[6^# - 7] &]

%o (PARI) is(n)=ispseudoprime(6^n-7) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A059614, A217351.

%K nonn,more,hard

%O 1,1

%A _Vincenzo Librandi_, Oct 02 2012

%E a(26)-a(27) from _Michael S. Branicky_, Jan 29 2023

%E a(28)-a(29) from _Michael S. Branicky_, Apr 10 2023

%E a(30) from _Michael S. Branicky_, Oct 27 2024