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 A275538 #14 May 26 2024 15:04:07 %S A275538 1,3,4,9,10,13,19,21,25,28,70,81,97,106,291,369,460,577,4705,5427, %T A275538 7153,7191,7885,12070,20794,34855 %N A275538 Numbers k such that (38*10^k + 547)/9 is prime. %C A275538 For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 2 followed by the digits 83 is prime (see Example section). %C A275538 a(27) > 10^5. %H A275538 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A275538 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 42w83</a>. %e A275538 3 is in this sequence because (38*10^3 + 547)/9 = 4283 is prime. %e A275538 Initial terms and associated primes: %e A275538 a(1) = 1, 103; %e A275538 a(2) = 3, 4283; %e A275538 a(3) = 4, 42283; %e A275538 a(4) = 9, 4222222283; %e A275538 a(5) = 10, 42222222283, etc. %t A275538 Select[Range[0, 100000], PrimeQ[(38*10^# + 547)/9] &] %o A275538 (PARI) isok(n) = isprime((38*10^n + 547)/9); \\ _Michel Marcus_, Aug 01 2016 %Y A275538 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A275538 nonn,more %O A275538 1,2 %A A275538 _Robert Price_, Aug 01 2016