A174178 - OEIS

%I #20 Sep 08 2022 08:45:51

%S 0,1,4,24,43,94,193,204,379,405,675,3811,10239,26809

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

%C a(15) > 10^5. - _Robert Price_, Mar 13 2015

%t Select[Range[0,5000], PrimeQ[(10^# + 2*# + 1)] &] (* _Vincenzo Librandi_, Oct 05 2012 *)

%o (Magma) [n: n in [0..400] | 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. A173840 (associated primes).

%K nonn,hard,more

%O 1,3

%A _Vincenzo Librandi_, Mar 11 2010

%E a(10)-a(12) from _Vincenzo Librandi_, Oct 05 2012

%E Prepended a(1)=0 and added a(13)-a(14) by _Robert Price_, Mar 13 2015