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%I #15 Jul 03 2023 00:58:54
%S 1,2,5,6,18,25,34,67,73,98,287,380,544,748,911,947,978,2480,3017,7951,
%T 13081,17665,17798,34857,43960,100566
%N Numbers k such that (26*10^k + 49)/3 is prime.
%C For k>1, numbers such that the digit 8 followed by k-2 occurrences of the digit 6 followed by the digits 83 is prime (see Example section).
%C a(27) > 3*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 86w83</a>.
%e 2 is in this sequence because (26*10^2 + 49)/3 = 883 is prime.
%e Initial terms and primes associated:
%e a(1) = 1, 103;
%e a(2) = 2, 883;
%e a(3) = 5, 866683;
%e a(4) = 6, 8666683;
%e a(5) = 18, 8666666666666666683; etc.
%t Select[Range[0, 100000], PrimeQ[(26*10^# + 49)/3] &]
%o (PARI) isok(k) = isprime((26*10^k + 49)/3); \\ _Michel Marcus_, Feb 18 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Feb 17 2017
%E a(26) from _Robert Price_, Jul 31 2019
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