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Numbers k such that 10^k + 987654321 is prime.
4

%I #21 Sep 08 2022 08:46:10

%S 6,11,15,27,42,113,135,186,207,503,2999,3005,3487,5718,7265,7629,

%T 11987,16063,27379,64770,73579,96504,116557

%N Numbers k such that 10^k + 987654321 is prime.

%C Note that 987654321 is the largest pandigital number in base-10, omitting 0.

%t Select[Range[1000], PrimeQ[10^# + 987654321] &] (* _Vincenzo Librandi_, Oct 12 2014 *)

%o (PARI) for(n=1,10^4,if(ispseudoprime(10^n+987654321),print1(n,", ")))

%o (Magma) [n: n in [1..500] | IsPrime(10^n+987654321)]; // _Vincenzo Librandi_, Oct 12 2014

%Y Cf. A248349, A248350, A248352, A050289.

%K nonn,hard,more

%O 1,1

%A _Derek Orr_, Oct 05 2014

%E a(9) corrected and a(19)-a(23) added by _Robert Price_, Dec 05 2019