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%I #8 Jun 16 2019 22:30:33
%S 0,1,3,4,9,12,13,15,30,37,58,67,142,355,442,660,1078,3337,5923,10204,
%T 21645,50149
%N Numbers k such that (52*10^k + 119)/9 is prime.
%C For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 7 followed by the digits 91 is prime (see Example section).
%C a(23) > 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 57w91</a>.
%e 3 is in this sequence because (52*10^3 + 119)/9 = 5791 is prime.
%e Initial terms and primes associated:
%e a(1) = 0, 19;
%e a(2) = 1, 71;
%e a(3) = 3, 5791;
%e a(4) = 4, 57791;
%e a(5) = 9, 5777777791; etc.
%t Select[Range[0, 100000], PrimeQ[(52*10^# + 119)/9] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,3
%A _Robert Price_, Oct 25 2017
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