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 A272195 #14 May 25 2024 15:04:58 %S A272195 1,2,4,5,7,8,13,16,22,112,134,139,250,445,475,512,544,1318,1588,3307, %T A272195 4216,4457,4474,4979,6241,9551,17939,20405,48106,54467,144797 %N A272195 Numbers k such that (64*10^k + 287)/9 is prime. %C A272195 For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 1 followed by the digits 43 is prime (see Example section). %C A272195 a(32) > 2*10^5. %H A272195 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A272195 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 71w43</a>. %e A272195 5 is in this sequence because (64*10^5 + 287)/9 = 711143 is prime. %e A272195 Initial terms and associated primes: %e A272195 a(1) = 1, 103; %e A272195 a(2) = 2, 743; %e A272195 a(3) = 4, 71143; %e A272195 a(4) = 5, 711143; %e A272195 a(5) = 7, 71111143, etc. %t A272195 Select[Range[0, 100000], PrimeQ[(64*10^#n + 287)/9] &] %o A272195 (PARI) lista(nn) = for(n=1, nn, if(ispseudoprime((64*10^n + 287)/9), print1(n, ", "))); \\ _Altug Alkan_, Apr 22 2016 %Y A272195 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A272195 nonn,more %O A272195 1,2 %A A272195 _Robert Price_, Apr 22 2016 %E A272195 a(31) from _Robert Price_, Apr 13 2019