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%I #14 Sep 15 2019 19:56:00
%S 1,2,4,5,8,13,14,26,44,58,61,83,256,878,1513,3122,6398,6476,8683,
%T 18482,33917,45937,64534
%N Numbers k such that (76*10^k + 113)/9 is prime.
%C For k > 1, numbers such that the digit 8 followed by k-2 occurrences of the digit 4 followed by the digits 57 is prime (see Example section).
%C a(24) > 2*10^5.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>.
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/primedifficulty.txt">Search for 84w57</a>.
%e 2 is in this sequence because (76*10^2 + 113)/9 = 857 is prime.
%e Initial terms and primes associated:
%e a(1) = 1, 97;
%e a(2) = 2, 857;
%e a(3) = 4, 84457;
%e a(4) = 5, 844457;
%e a(5) = 8, 844444457; etc.
%t Select[Range[0, 100000], PrimeQ[(76*10^# + 113)/9] &] (* Corrected by _Georg Fischer_, Jul 22 2019 *)
%o (PARI) isok(k) = isprime((76*10^k + 113)/9); \\ _Michel Marcus_, Nov 12 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Nov 11 2017
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