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 A281171 #11 Jun 07 2024 23:59:15 %S A281171 1,2,5,9,13,20,21,32,33,56,73,81,149,313,455,753,1013,1166,1304,1679, %T A281171 15758,15896,21801,41353,45421,131090,151007 %N A281171 Numbers k such that (5*10^k + 37)/3 is prime. %C A281171 For k > 1, numbers k such that the digit 1 followed by k-2 occurrences of the digit 6 followed by the digits 79 is prime (see Example section). %C A281171 a(28) > 2*10^5. %H A281171 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A281171 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 16w79</a>. %e A281171 2 is in this sequence because (5*10^2 + 37) / 3 = 179 is prime. %e A281171 Initial terms and associated primes: %e A281171 a(1) = 1, 29; %e A281171 a(2) = 2, 179; %e A281171 a(3) = 5, 166679; %e A281171 a(4) = 9, 1666666679; %e A281171 a(5) = 13, 16666666666679; etc. %t A281171 Select[Range[0, 100000], PrimeQ[(5*10^# + 37) / 3] &] %Y A281171 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A281171 nonn,more,hard %O A281171 1,2 %A A281171 _Robert Price_, Jan 16 2017 %E A281171 a(26)-a(27) from _Robert Price_, Mar 02 2018