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%I #16 May 25 2024 14:28:05
%S 1,7,13,44,73,128,152,245,408,436,618,638,884,1405,1502,1656,2292,
%T 2318,4212,5712,5868,13837,18648,25102,30742,34532,53951,159258
%N Numbers k such that 89*10^k - 9 is prime.
%C For k > 0, numbers k such that the digits 88 followed by k-1 occurrences of the digit 9 followed by the digit 1 is prime (see Example section).
%C a(29) > 3*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/prime_difficulty.txt">Search for 889w1</a>.
%e 7 is in this sequence because 89*10^7 - 9 = 889999991 is prime.
%e Initial terms and associated primes:
%e a(1) = 1, 881;
%e a(2) = 7, 889999991;
%e a(3) = 13, 889999999999991;
%e a(4) = 44, 8899999999999999999999999999999999999999999991; etc.
%t Select[Range[0, 100000], PrimeQ[89*10^# - 9] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, May 29 2017
%E a(28) from _Robert Price_, May 12 2020
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