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 A290964 #14 May 19 2024 21:54:59 %S A290964 3,5,6,14,24,84,87,207,734,797,1743,2211,3539,5871,5949,6954,8309, %T A290964 10896,12771,22382,35112,38267,69866,121229,125754,133979 %N A290964 Numbers k such that (35*10^k - 593)/9 is prime. %C A290964 For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 8 followed by the digits 23 is prime (see Example section). %C A290964 a(27) > 2*10^5. %H A290964 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A290964 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 38w23</a>. %e A290964 5 is in this sequence because (35*10^5 - 593)/9 = 388823 is prime. %e A290964 Initial terms and associated primes: %e A290964 a(1) = 3, 3823; %e A290964 a(2) = 5, 388823; %e A290964 a(3) = 6, 3888823; %e A290964 a(4) = 14; 388888888888823; %e A290964 a(5) = 24, 3888888888888888888888823; etc. %t A290964 Select[Range[2, 100000], PrimeQ[(35*10^# - 593)/9] &] %o A290964 (PARI) isok(n) = ispseudoprime((35*10^n - 593)/9) \\ _Altug Alkan_, Aug 15 2017 %Y A290964 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A290964 nonn,more,hard %O A290964 1,1 %A A290964 _Robert Price_, Aug 15 2017 %E A290964 a(24)-a(26) from _Robert Price_, Jul 18 2018