This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A282456 #11 Jun 08 2024 05:44:19 %S A282456 0,1,2,4,9,12,21,55,307,332,388,820,1593,2432,2438,3372,6270,7437, %T A282456 8268,12135,16588,41397,46126,47910,81091 %N A282456 Numbers k such that 18*10^k + 1 is prime. %C A282456 For k > 0, numbers k such that the digits 18 followed by k-1 occurrences of the digit 0 followed by the digit 1 is prime (see Example section). %C A282456 a(26) > 10^5. %H A282456 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A282456 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 180w1</a>. %e A282456 2 is in this sequence because 18*10^2 + 1 = 1801 is prime. %e A282456 Initial terms and associated primes: %e A282456 a(1) = 0, 19; %e A282456 a(2) = 1, 181; %e A282456 a(3) = 2, 1801; %e A282456 a(4) = 4, 180001; %e A282456 a(5) = 9, 18000000001; etc. %t A282456 Select[Range[0, 100000], PrimeQ[18*10^# + 1] &] %Y A282456 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A282456 nonn,more,hard %O A282456 1,3 %A A282456 _Robert Price_, Feb 15 2017