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%I #15 Jun 02 2024 20:58:49
%S 1,3,4,6,7,9,16,45,73,75,94,217,241,294,1074,2133,2379,3504,8241,
%T 16218,16387,18135,31771,47331,58456,72696,76672
%N Numbers k such that (47*10^k + 133)/9 is prime.
%C For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 2 followed by the digits 37 is prime (see Example section).
%C a(28) > 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/prime_difficulty.txt">Search for 52w37</a>.
%e 4 is in this sequence because (47*10^4 + 133)/9 = 52237 is prime.
%e Initial terms and associated primes:
%e a(1) = 1, 67;
%e a(2) = 3, 5237;
%e a(3) = 4, 52237;
%e a(4) = 6, 5222237;
%e a(5) = 7, 52222237; etc.
%t Select[Range[0, 100000], PrimeQ[(47*10^# + 133)/9] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Apr 17 2017