login
Numbers n such that (2^(n+7)*5^(n+6)-1024877)/9 is prime (n > 0).
0

%I #30 Sep 08 2022 08:46:15

%S 1,27,37,42,94,117,667,1413,1764,4138,8341,9337,10737,16132,17425

%N Numbers n such that (2^(n+7)*5^(n+6)-1024877)/9 is prime (n > 0).

%C Numbers n such that '108347' (prime) appended to n times the digit 2 is prime.

%C a(n) mod 3 <= 1.

%e 1 appears because 2108347 ('2' prepended to '108347') is prime.

%t Select[ Range[2000], PrimeQ[(2^(#+7) * 5^(#+6) - 1024877) / 9] &] (*Or*)

%t Select[ Range[2000], PrimeQ[5*(2^(#+7) * 5^(#+5) - 204979) / 9 + 2] &]

%o (Magma) [n: n in [1..700] |IsPrime((2^(n+7)*5^(n+6)-1024877) div 9)]; // _Vincenzo Librandi_, Jan 13 2016

%o (PARI) is(n) = ispseudoprime((2^(n+7)*5^(n+6) - 1024877) / 9); \\ _Altug Alkan_, Jan 15 2016

%K nonn,base,more

%O 1,2

%A _Mikk Heidemaa_, Jan 07 2016