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%I #15 Jan 17 2019 13:44:08
%S 1,2,3,4,5,11,28,40,65,95,187,201,202,211,316,331,559,746,1307,2139,
%T 3571,5843,6545,12717,32804,46389,72326,135301
%N Numbers k such that (14*10^k - 53) / 3 is prime.
%C For k>1, numbers such that the digit 4 followed by k-2 occurrences of the digit 6 followed by the digits 49 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/primedifficulty.txt">Search for 46w49.</a>
%e 3 is in this sequence because (14*10^3 - 53) / 3 = 4649 is prime.
%e Initial terms and primes associated:
%e a(1) = 1, 29;
%e a(2) = 2, 449;
%e a(3) = 3, 4649;
%e a(4) = 4, 46649;
%e a(5) = 5, 466649; etc.
%t Select[Range[1, 100000], PrimeQ[(14*10^# - 53) / 3] &]
%o (PARI) is(n)=ispseudoprime((14*10^n - 53)/3) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Dec 28 2016
%E a(28) from _Robert Price_, Dec 17 2018
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