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 A273371 #19 May 02 2024 04:24:39 %S A273371 1,2,3,6,9,15,21,26,33,42,131,168,434,464,501,1004,1011,1089,1509, %T A273371 2025,2283,2526,9150,9464,14139,14827,18941,32426,36719,42933,138569 %N A273371 Numbers k such that (17*10^k - 77)/3 is prime. %C A273371 For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 6 followed by the digits 41 is prime (see Example section). %C A273371 a(32) > 3*10^5. %H A273371 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A273371 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 56w41</a>. %e A273371 3 is in this sequence because (17*10^3-77)/3 = 5641 is prime. %e A273371 Initial terms and associated primes: %e A273371 a(1) = 1, 31; %e A273371 a(2) = 2, 541; %e A273371 a(3) = 3, 5641; %e A273371 a(4) = 6, 5666641; %e A273371 a(5) = 9, 5666666641, etc. %t A273371 Select[Range[0, 100000], PrimeQ[(17*10^# - 77)/3] &] %o A273371 (PARI) is(n)=ispseudoprime((17*10^n - 77)/3) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A273371 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A273371 nonn,more %O A273371 1,2 %A A273371 _Robert Price_, May 20 2016 %E A273371 a(31) from _Robert Price_, Aug 21 2019