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%I #17 Feb 11 2023 13:53:17
%S 2,4,184,460,784,3248,5194,92386
%N Numbers k such that 10^k + 111 is prime.
%C Terms must be congruent to 2 or 4 mod 6. Other than the first term, which produces 10^2 + 111 = 211, these terms produce primes whose decimal representation is 1 <n-3 0's> 111 concatenated. These are only known to be highly probable primes for 184 and beyond. No more terms up to 15000.
%C a(8) > 55000. - _Tyler NeSmith_, Jul 10 2021
%C The corresponding primes have digit sum 4 (A062339). - _Jeppe Stig Nielsen_, Feb 10 2023
%C a(9) > 10^5. - _Jeppe Stig Nielsen_, Feb 11 2023
%e As 10111 = 10^4 + 111 is a prime, 4 is a term.
%t Select[Range[5200], PrimeQ[10^# + 111] &] (* _G. C. Greubel_, Oct 21 2018 *)
%o (PARI) is(k)=ispseudoprime(10^k+111) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A096912, A157711, A062339, A020449, A036929, A161786.
%K nonn,more
%O 1,1
%A _Rick L. Shepherd_, Sep 21 2009
%E a(8) from _Jeppe Stig Nielsen_, Feb 10 2023
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