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%I #19 Jan 17 2019 13:44:09
%S 3,9,10,28,41,58,62,86,192,209,566,1227,1566,1995,2003,3654,4271,6107,
%T 6281,8997,24412,32970,65944,85782,112742,115910,141718
%N Numbers k such that (11*10^k - 131)/3 is prime.
%C For k>1, numbers such that the digit 3 followed by k-2 occurrences of the digit 6 followed by the digits 23 is prime (see Example section).
%C a(28) > 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 36w23.</a>
%e 3 is in this sequence because (11*10^3 - 131)/3 = 3623 is prime.
%e Initial terms and primes associated:
%e a(1) = 3, 3623;
%e a(2) = 9, 3666666623;
%e a(3) = 10, 36666666623;
%e a(4) = 28, 36666666666666666666666666623;
%e a(5) = 41, 366666666666666666666666666666666666666623; etc.
%t Select[Range[2, 100000], PrimeQ[(11*10^# - 131)/3] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,1
%A _Robert Price_, Feb 23 2017
%E a(25)-a(27) from _Robert Price_, Sep 28 2018
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