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%I #11 May 25 2024 19:37:35
%S 2,3,5,6,8,11,29,99,134,407,516,986,1482,2709,3326,4395,5277,11712,
%T 13067,22542,50414,70616,110006
%N Numbers k such that (7*10^k - 151)/9 is prime.
%C For k > 1, numbers k such that k-2 occurrences of the digit 7 followed by the digits 61 is prime (see Example section).
%C a(24) > 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 7w61</a>.
%e 3 is in this sequence because (7*10^3 - 151)/9 = 761 is prime.
%e Initial terms and associated primes:
%e a(1) = 2, 61;
%e a(2) = 3, 761;
%e a(3) = 5, 77761;
%e a(4) = 6, 777761;
%e a(5) = 8, 77777761; etc.
%t Select[Range[2, 100000], PrimeQ[(7*10^# - 151)/9] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard,changed
%O 1,1
%A _Robert Price_, Sep 28 2017
%E a(23) from _Robert Price_, Feb 14 2018
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