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%I #14 May 25 2024 17:40:28
%S 0,1,2,8,10,17,18,30,37,42,47,100,286,287,440,1074,1124,2298,2879,
%T 4948,4950,12730,17429,31768,47726,64220,80200,127240
%N Numbers k such that (26*10^k + 61)/3 is prime.
%C For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 6 followed by the digits 87 is prime (see Example section).
%C a(29) > 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 86w87</a>.
%e 2 is in this sequence because (26*10^2 + 61)/3 = 887 is prime.
%e Initial terms and associated primes:
%e a(1) = 0, 29;
%e a(2) = 1, 107;
%e a(3) = 2, 887;
%e a(4) = 8, 866666687;
%e a(5) = 10, 86666666687; etc.
%t Select[Range[0, 100000], PrimeQ[(26*10^# + 61)/3] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,3
%A _Robert Price_, Jun 17 2017
%E a(28) from _Robert Price_, Oct 13 2019
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