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Numbers n such that 9^n-8 is prime.
5

%I #30 Sep 08 2022 08:45:53

%S 2,4,7,10,11,31,127,136,215,953,1139,1799,3406,7633,13090,13171,13511,

%T 32593

%N Numbers n such that 9^n-8 is prime.

%C a(19) > 2*10^5. - _Robert Price_, Jul 29 2015

%p A177093:=n->`if`(isprime(9^n-8), n, NULL): seq(A177093(n), n=1..10^3); # _Wesley Ivan Hurt_, Nov 14 2014

%t Select[Range[1000], PrimeQ[9^#-8] &] (* _Vincenzo Librandi_, Nov 15 2014 *)

%o (Magma) [n: n in [1..900]| IsPrime(9^n-8)]

%o (PARI) is(n)=isprime(9^n-8) \\ _Charles R Greathouse IV_, Nov 15 2014

%Y Cf. A177094.

%K nonn,more

%O 1,1

%A _Vincenzo Librandi_, Nov 15 2010

%E Extended and crossref added by _D. S. McNeil_, Nov 15 2010

%E a(14)-a(18) from _Robert Price_, Jul 29 2015