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%I #11 Jan 17 2019 13:44:08
%S 1,2,3,6,10,12,18,34,42,61,76,85,94,178,348,451,1123,1455,2234,4519,
%T 7502,16036,24216,156522
%N Numbers k such that (13*10^k + 89) / 3 is prime.
%C For k>1, numbers such that the digit 4 followed by k-2 occurrences of the digit 3 followed by the digits 63 is prime (see Example section).
%C a(25) > 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 43w63.</a>
%e 3 is in this sequence because (13*10^3 + 89) / 3 = 4363 is prime.
%e Initial terms and primes associated:
%e a(1) = 1, 73;
%e a(2) = 2, 463;
%e a(3) = 3, 4363;
%e a(4) = 6, 4333363;
%e a(5) = 10, 43333333363; etc.
%t Select[Range[0, 100000], PrimeQ[(13*10^# + 89) / 3] &]
%o (PARI) is(n)=ispseudoprime((13*10^n + 89)/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_, Jan 05 2017
%E a(24) from _Robert Price_, Sep 10 2018
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