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 A275525 #29 May 25 2024 15:38:40 %S A275525 2,3,5,6,11,12,26,32,36,75,137,143,279,290,363,716,770,1377,1638,4470, %T A275525 5952,10526,15132,27054,81485 %N A275525 Numbers k such that (73*10^k + 107)/9 is prime. %C A275525 For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 1 followed by the digits 23 is prime (see Example section). %C A275525 a(26) > 10^5. %H A275525 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A275525 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 81w23</a>. %e A275525 3 is in this sequence because (73*10^3+107)/9 = 8123 is prime. %e A275525 Initial terms and associated primes: %e A275525 a(1) = 2, 823; %e A275525 a(2) = 3, 8123; %e A275525 a(3) = 5, 811123; %e A275525 a(4) = 6, 8111123; %e A275525 a(5) = 11, 811111111123, etc. %t A275525 Select[Range[0, 100000], PrimeQ[(73*10^#+107)/9] &] %o A275525 (PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((73*10^n+107)/9), print1(n, ", "))); \\ _Altug Alkan_, Aug 11 2016 %Y A275525 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A275525 nonn,more %O A275525 1,1 %A A275525 _Robert Price_, Aug 11 2016