%I #12 May 18 2024 11:32:17
%S 1,2,3,4,6,8,16,24,32,103,1436,6144,6472,6951,8920,9598,12028,13803,
%T 21867,23893,46140
%N Numbers k such that 9*10^k + 67 is prime.
%C For k>1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 0 followed by the digits 67 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 90w67</a>.
%e 2 is in this sequence because 9*10^2 + 67 = 967 is prime.
%e Initial terms and associated primes:
%e a(1) = 1, 157;
%e a(2) = 2, 967;
%e a(3) = 3, 9067;
%e a(4) = 4, 90067;
%e a(5) = 6, 90067; etc.
%t Select[Range[0, 100000], PrimeQ[9*10^# + 67] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Nov 06 2017