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 A291609 #12 Jun 02 2024 20:58:59 %S A291609 1,3,4,7,10,24,37,46,63,64,91,114,367,453,1156,1347,1524,7153,10893, %T A291609 13548,15153,43093,61167,184993 %N A291609 Numbers k such that (49*10^k - 67)/9 is prime. %C A291609 For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 4 followed by the digits 37 is prime (see Example section). %C A291609 a(25) > 2*10^5. %H A291609 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A291609 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 54w37</a>. %e A291609 4 is in this sequence because (49*10^4 - 67)/9 = 54437 is prime. %e A291609 Initial terms and associated primes: %e A291609 a(1) = 1, 47; %e A291609 a(2) = 3, 5437; %e A291609 a(3) = 4, 54437; %e A291609 a(4) = 7, 54444437; %e A291609 a(5) = 10, 54444444437; etc. %t A291609 Select[Range[1, 100000], PrimeQ[(49*10^# - 67)/9] &] %Y A291609 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A291609 nonn,more,hard %O A291609 1,2 %A A291609 _Robert Price_, Aug 27 2017 %E A291609 a(24) from _Robert Price_, Mar 15 2019