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 A272717 #36 May 02 2024 04:24:18 %S A272717 1,5,7,17,35,46,56,148,187,190,256,551,553,1033,1751,1976,2696,3116, %T A272717 3364,5353,5893,8063,9548,10640,24655,77992 %N A272717 Numbers k such that (65*10^k + 691)/9 is prime. %C A272717 For k > 1, numbers k such that the digit 7 followed by k-2 occurrences of the digit 2 followed by the digits 99 is prime (see Example section). %C A272717 a(27) > 10^5. %H A272717 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A272717 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 72w99</a>. %e A272717 5 is in this sequence because (65*10^5+691)/9 = 722299 is prime. %e A272717 Initial terms and associated primes: %e A272717 a(1) = 1, 149; %e A272717 a(2) = 5, 722299; %e A272717 a(3) = 7, 72222299; %e A272717 a(4) = 17, 722222222222222299; %e A272717 a(5) = 35, 722222222222222222222222222222222299, etc. %t A272717 Select[Range[0, 100000], PrimeQ[(65*10^#+691)/9] &] %o A272717 (PARI) is(n)=ispseudoprime((65*10^n+691)/9) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A272717 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A272717 nonn,more %O A272717 1,2 %A A272717 _Robert Price_, Aug 11 2016