%I #22 Jun 09 2024 18:06:28
%S 2,3,4,9,22,50,67,82,87,89,130,134,170,179,220,832,1425,1648,2356,
%T 2434,6556,11391,12610,20278,46509,50253
%N Numbers k such that 8*10^k - 99 is prime.
%C For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 9 followed by the digits 01 is prime (see Example section).
%C a(27) > 3*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 79w01</a>.
%e 3 is in this sequence because 8*10^3-99 = 7901 is prime.
%e Initial terms and associated primes:
%e a(1) = 2, 701;
%e a(2) = 3, 7901;
%e a(3) = 4, 79901;
%e a(4) = 9, 7999999901;
%e a(5) = 22, 79999999999999999999901; etc.
%t Select[Range[2, 100000], PrimeQ[8*10^#-99] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,1
%A _Robert Price_, Feb 21 2017