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 A276642 #58 Jun 02 2024 14:03:46 %S A276642 2,3,4,5,6,8,10,14,15,62,98,184,190,389,430,815,918,1124,1284,9544, %T A276642 10068,16514,24756,39880,86478,179138 %N A276642 Numbers k such that 3*10^k + 89 is prime. %C A276642 For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 0 followed by the digits 89 is prime (see Example section). %C A276642 a(27) > 2*10^5. %H A276642 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A276642 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 30w89</a>. %e A276642 3 is in this sequence because 3*10^3 + 89 = 3089 is prime. %e A276642 Initial terms and associated primes: %e A276642 a(1) = 2, 389; %e A276642 a(2) = 3, 3089; %e A276642 a(3) = 4, 30089; %e A276642 a(4) = 5, 300089; %e A276642 a(5) = 6, 3000089; etc. %t A276642 Select[Range[0, 100000], PrimeQ[3*10^# + 89] &] %o A276642 (PARI) isok(k) = ispseudoprime(3*10^k + 89); \\ _Altug Alkan_, Mar 30 2018 %Y A276642 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A276642 nonn,more,hard %O A276642 1,1 %A A276642 _Robert Price_, Mar 23 2017 %E A276642 a(26) from _Robert Price_, Oct 22 2018