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%I #15 May 03 2024 07:45:25
%S 1,3,4,10,81,135,217,232,247,250,325,579,955,1288,1522,1839,2794,
%T 15658,15777,54547,63790
%N Numbers k such that (44*10^k - 161)/9 is prime.
%C For k > 1, numbers k such that the digit 4 followed by k - 2 occurrences of the digit 8 followed by the digits 71 is prime (see Example section).
%C a(22) > 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 48w71</a>.
%e 3 is in this sequence because (44*10^3 - 161)/9 = 4871 is prime.
%e Initial terms and associated primes:
%e a(1) = 1, 31;
%e a(2) = 3, 4871;
%e a(3) = 4, 48871;
%e a(4) = 10, 48888888871; etc.
%t Select[Range[1, 100000], PrimeQ[(44*10^# - 161)/9] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Nov 28 2017