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%I #8 Jul 27 2019 12:08:33
%S 1,2,4,13,16,19,25,44,55,64,69,183,241,290,345,398,410,423,860,1287,
%T 2398,2553,3109
%N Numbers k such that 9*10^k - 23 is prime.
%C For k>1, numbers such that the digit 8 followed by k-2 occurrences of the digit 9 followed by the digits 77 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 89w77</a>.
%e 4 is in this sequence because 9*10^4 - 23 = 89977 is prime.
%e Initial terms and primes associated:
%e a(1) = 1, 67;
%e a(2) = 2, 877;
%e a(3) = 4, 89977;
%e a(4) = 13, 89999999999977;
%e a(5) = 16, 89999999999999977; etc.
%t Select[Range[1, 100000], PrimeQ[9*10^# - 23] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, May 29 2017
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