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%I #21 Jan 17 2019 13:44:08
%S 0,1,2,3,4,7,9,57,98,122,123,249,304,318,339,374,390,476,619,1358,
%T 1724,3351,5046,5572,6685,9421,14362,97353
%N Numbers n such that (26*10^n + 31)/3 is prime.
%C For n>1, numbers n such that the digit 8 followed by n-2 occurrences of the digit 6 followed by the digits 77 is prime (see Example section).
%C a(29) > 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 86w77.</a>
%e 3 is in this sequence because (26*10^3 + 31)/3 = 877 is prime.
%e Initial terms and primes associated:
%e a(1) = 0, 19;
%e a(2) = 1, 97;
%e a(3) = 2, 877;
%e a(4) = 3, 8677;
%e a(5) = 4, 86677, etc.
%t Select[Range[0, 100000], PrimeQ[(26*10^# + 31)/3] &]
%o (PARI) is(n)=ispseudoprime((26*10^n+31)/3) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more
%O 1,3
%A _Robert Price_, Jul 14 2016
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