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 A273728 #22 May 26 2024 14:58:41 %S A273728 1,2,3,5,7,12,37,45,55,139,205,264,445,975,1111,1298,1340,1835,2264, %T A273728 2317,2897,2955,3001,4134,6637,7063,20613,114795,147890 %N A273728 Numbers k such that (17*10^k + 79)/3 is prime. %C A273728 For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 6 followed by the digits 93 is prime (see Example section). %C A273728 a(30) > 3*10^5. - _Robert Price_, Jul 10 2023 %H A273728 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A273728 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 56w93</a>. %e A273728 3 is in this sequence because (17*10^3+79)/3 = 5693 is prime. %e A273728 Initial terms and associated primes: %e A273728 a(1) = 1, 83; %e A273728 a(2) = 2, 593; %e A273728 a(3) = 3, 5693; %e A273728 a(4) = 5, 566693; %e A273728 a(5) = 7, 56666693, etc. %t A273728 Select[Range[0, 100000], PrimeQ[(17*10^# + 79)/3] &] %o A273728 (PARI) is(n)=ispseudoprime((17*10^n + 79)/3) \\ _Charles R Greathouse IV_, Jun 08 2016 %Y A273728 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A273728 nonn,more %O A273728 1,2 %A A273728 _Robert Price_, May 28 2016 %E A273728 a(28)-a(29) from _Robert Price_, Apr 15 2019