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%I #14 Jan 17 2019 13:44:08
%S 4,6,13,15,23,25,31,71,133,333,341,905,1027,3667,7241,8217,8493,9816,
%T 11842,15454,15891,19117,30424,35196,42808,78408,95641,177466
%N Numbers k such that (11*10^k - 113) / 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 29 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 36w29.</a>
%e 6 is in this sequence because (11*10^6 - 113) / 3 = 3666629 is prime.
%e Initial terms and primes associated:
%e a(1) = 4, 36629;
%e a(2) = 6, 3666629;
%e a(3) = 13, 36666666666629;
%e a(4) = 15, 3666666666666629;
%e a(5) = 23, 366666666666666666666629; etc.
%t Select[Range[2, 100000], PrimeQ[(11*10^# - 113) / 3] &]
%o (PARI) is(n)=ispseudoprime((11*10^n - 113)/3) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,1
%A _Robert Price_, Jan 05 2017
%E a(28) from _Robert Price_, Oct 10 2018
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