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%I #12 Jun 09 2024 22:01:23
%S 2,3,11,15,23,26,46,68,76,111,146,147,444,843,896,1390,2242,3131,4251,
%T 4252,6299,58815,93692
%N Numbers k such that 7*10^k - 83 is prime.
%C For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 9 followed by the digits 17 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/prime_difficulty.txt">Search for 69w17</a>.
%e 3 is in this sequence because 7*10^3 - 83 = 6917 is prime.
%e Initial terms and associated primes:
%e a(1) = 2, 617;
%e a(2) = 3, 6917;
%e a(3) = 11, 699999999917;
%e a(4) = 15, 6999999999999917;
%e a(5) = 23, 699999999999999999999917; etc.
%t Select[Range[1, 100000], PrimeQ[7*10^# - 83] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,1
%A _Robert Price_, Sep 28 2017
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