The OEIS is supported by the many generous donors to the OEIS Foundation.
%I #12 May 25 2024 16:58:23
%S 1,2,8,9,12,17,23,26,51,113,236,509,1659,2769,5258,8456,8787,11487,
%T 19367,28094,36114,69663,115697
%N Numbers k such that (44*10^k - 413)/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 43 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 48w43</a>.
%e 2 is in this sequence because (44*10^2 - 413)/9 = 443 is prime.
%e Initial terms and associated primes:
%e a(1) = 1, 3;
%e a(2) = 2, 443;
%e a(3) = 8, 488888843;
%e a(4) = 9, 4888888843;
%e a(5) = 12, 4888888888843; etc.
%t Select[Range[1, 100000], PrimeQ[(44*10^# - 413)/9] &]
%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
%K nonn,more,hard
%O 1,2
%A _Robert Price_, Oct 29 2017
%E a(23) from _Robert Price_, Mar 03 2019