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Numbers n such that 10^n-2*n+1 is prime.
5

%I #14 Sep 08 2022 08:45:51

%S 2,5,14,42,72,74,354,1176,1274,4815,6885,28214

%N Numbers n such that 10^n-2*n+1 is prime.

%C a(13) > 10^5. - _Robert Price_, Mar 26 2015

%t Select[Range[5000], PrimeQ[(10^# - 2 # + 1)] &] (* _Vincenzo Librandi_, Oct 05 2012 *)

%o (Magma) /* The code gives only the terms up to 354: */ [n: n in [1..600] | IsPrime(10^n-2*n+1) ]

%o (PARI) is(n)=ispseudoprime(10^n-2*n+1) \\ _Charles R Greathouse IV_, Feb 20 2017

%Y Cf. A173837, A110065, A110066, A110067.

%K nonn,more

%O 1,1

%A _Vincenzo Librandi_, Mar 11 2010

%E a(8)-a(10) from _Vincenzo Librandi_, Oct 05 2012

%E a(11)-a(12) from _Robert Price_, Mar 26 2015