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%I #11 Feb 05 2020 19:47:53
%S 0,1,6,13,18,28,40,45,50,70,101,210,248,298,1246,1340,1586,2466,6548,
%T 6713,7394,23904,32450,38171,39120,67816,108610,112400,129038
%N Numbers k such that (134*10^k + 7)/3 is prime.
%C For k>0, numbers such that the digits 44 followed by k-1 occurrences of the digit 6 followed by the digit 9 is prime (see Example section).
%C a(30) > 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 446w9</a>.
%e 1 is in this sequence because (134*10^1 + 7)/3 = 449 is prime.
%e Initial terms and primes associated:
%e a(1) = 0, 47;
%e a(2) = 1, 449;
%e a(3) = 6, 44666669;
%e a(4) = 13, 446666666666669;
%e a(5) = 18, 44666666666666666669; etc.
%t Select[Range[0, 100000], PrimeQ[(134*10^# + 7)/3] &]
%o (PARI) isok(k) = isprime((134*10^k + 7)/3); \\ _Michel Marcus_, Feb 26 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,3
%A _Robert Price_, Feb 26 2017
%E a(27)-a(29) from _Robert Price_, Feb 05 2020
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