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%I #10 Jul 27 2019 12:06:50
%S 1,3,7,9,10,13,76,93,141,202,274,445,907,1233,1366,2131,2590,2979,
%T 3489,3735,95277,148306,165663
%N Numbers k such that (71*10^k - 539)/9 is prime.
%C For k > 1, numbers such that the digit 7 followed by k-2 occurrences of the digit 8 followed by the digits 29 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 78w29</a>.
%e 3 is in this sequence because (71*10^3 - 539)/9 = 7829 is prime.
%e Initial terms and primes associated:
%e a(1) = 1, 19;
%e a(2) = 3, 7829;
%e a(3) = 7, 78888829;
%e a(4) = 9, 7888888829;
%e a(5) = 10, 78888888829; etc.
%t Select[Range[1, 100000], PrimeQ[(71*10^#- 539)/9] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Nov 02 2017
%E a(22)-a(23) from _Robert Price_, Jul 27 2019
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