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%I #9 May 31 2019 02:58:26
%S 2,3,9,15,39,45,59,137,180,224,264,476,491,504,1905,3144,4784,10893,
%T 24483,28602,82706,100283,129789,131886,132125
%N Numbers k such that (47*10^k - 119)/9 is prime.
%C For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 2 followed by the digits 09 is prime (see Example section).
%C a(26) > 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 52w09</a>.
%e 3 is in this sequence because (47*10^3 - 119)/9 = 5209 is prime.
%e Initial terms and primes associated:
%e a(1) = 2, 509;
%e a(2) = 3, 5209;
%e a(3) = 9, 5222222209;
%e a(4) = 15, 5222222222222209;
%e a(5) = 39, 5222222222222222222222222222222222222209; etc.
%t Select[Range[1, 100000], PrimeQ[(47*10^# - 119)/9] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,1
%A _Robert Price_, Sep 04 2017
%E a(22)-a(25) from _Robert Price_, May 30 2019
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