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%I #9 Jan 17 2019 13:44:10
%S 2,3,9,18,21,99,311,437,687,761,1451,2088,2559,2898,4974,5058,5798,
%T 6776
%N Numbers k such that (41*10^k - 329)/9 is prime.
%C For k > 1, numbers such that the digit 4 followed by k-2 occurrences of the digit 5 followed by the digits 19 is prime (see Example section).
%C a(19) > 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 45w19</a>
%e 2 is in this sequence because (41*10^2 - 329)/9 = 419 is prime.
%e Initial terms and primes associated:
%e a(1) = 2, 419;
%e a(2) = 3, 4519;
%e a(3) = 9, 4555555519;
%e a(4) = 18, 4555555555555555519;
%e a(5) = 21, 4555555555555555555519; etc.
%t Select[Range[1, 100000], PrimeQ[(41*10^# - 329)/9] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,1
%A _Robert Price_, Dec 03 2017
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