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 A274037 #16 May 02 2024 04:27:02 %S A274037 2,5,6,10,16,29,35,82,107,170,185,204,223,226,388,512,1586,2137,3182, %T A274037 7325,7346,8143,8746,11322,11497,13279,44681,108624,183872 %N A274037 Numbers k such that 3*10^k - 49 is prime. %C A274037 For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 9 followed by the digits 51 is prime (see Example section). %C A274037 a(31) > 2*10^5. %H A274037 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A274037 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 29w51</a>. %e A274037 5 is in this sequence because 3*10^5-49 = 299951 is prime. %e A274037 Initial terms and associated primes: %e A274037 a(1) = 2, 251; %e A274037 a(2) = 5, 299951; %e A274037 a(3) = 6, 2999951; %e A274037 a(4) = 10, 29999999951; %e A274037 a(5) = 16, 29999999999999951, etc. %t A274037 Select[Range[0, 100000], PrimeQ[3*10^# - 49] &] %o A274037 (PARI) is(n)=ispseudoprime(3*10^n - 49) \\ _Charles R Greathouse IV_, Jun 08 2016 %Y A274037 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A274037 nonn,more %O A274037 1,1 %A A274037 _Robert Price_, Jun 07 2016 %E A274037 a(28)-a(29) from _Robert Price_, Jul 29 2018