|
%I #16 Sep 08 2022 08:46:14
%S 1,2,12,14,110,2574,10964,24257,44364
%N Numbers n such that 49^n - 7^n - 1 is prime.
%C For n = 1, 2, 12, 14 the corresponding primes are 41, 2351, 191581231366725127199, 459986536544061737903951.
%C a(10) > 10^5. - _Robert Price_, Dec 25 2019
%e 2 is in the sequence because 49^2 - 7^2 - 1 = 2351 is prime.
%t Select[Range[2000], PrimeQ[49^# - 7^# - 1] &]
%o (Magma) [n: n in [0..1000] | IsPrime(49^n - 7^n - 1)];
%o (PARI) for(n=1, 1e3, if(ispseudoprime(49^n - 7^n - 1), print1(n, ", "))) \\ _Altug Alkan_, Dec 12 2015
%Y Cf. similar sequences listed in A265481.
%K nonn,more
%O 1,2
%A _Vincenzo Librandi_, Dec 12 2015
%E a(6) from _Ray Chandler_, Sep 25 2019
%E a(7)-a(9) from _Robert Price_, Dec 25 2019
| 