A174175 - OEIS

%I #13 Sep 08 2022 08:45:51

%S 1,2,4,10,20,35,91,112,116,325,367,674,2440,14099,38315,47989

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

%C a(17) > 10^5. - _Robert Price_, Mar 24 2015

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

%o (Magma) /* The code gives only the terms up to 367: */ [n: n in [1..500] | IsPrime(10^n+2*n-1)];

%o (PARI) is(n)=ispseudoprime(10^n+2*n-1) \\ _Charles R Greathouse IV_, Jun 06 2017

%Y Cf. A173851 (accociated primes).

%K nonn,more

%O 1,2

%A _Vincenzo Librandi_, Mar 11 2010

%E a(11)-a(13) from _Vincenzo Librandi_, Oct 05 2012

%E a(14)-a(16) from _Robert Price_, Mar 24 2015