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%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