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 A272622 #23 May 02 2024 04:24:07 %S A272622 1,2,4,5,10,14,25,34,40,63,74,129,149,345,370,425,477,627,951,1610, %T A272622 2564,2689,4227,7300,7444,8360,16541,21187,25685,31803,89858,92821 %N A272622 Numbers k such that 9*10^k + 19 is prime. %C A272622 For k > 1, numbers k such that the digit 9 followed by k-2 occurrences of the digit 0 followed by the digits 19 is prime (see Example section). %C A272622 a(33) > 3*10^5. %H A272622 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A272622 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 90w19</a>. %e A272622 4 is in this sequence because 9*10^4+19 = 90019 is prime. %e A272622 Initial terms and associated primes: %e A272622 a(1) = 1, 109; %e A272622 a(2) = 2, 919; %e A272622 a(3) = 4, 90019; %e A272622 a(4) = 5, 900019; %e A272622 a(5) = 10, 90000000019, etc. %t A272622 Select[Range[0, 100000], PrimeQ[9*10^# + 19] &] %o A272622 (PARI) is(n)=ispseudoprime(9*10^n + 19) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A272622 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A272622 nonn,more %O A272622 1,2 %A A272622 _Robert Price_, May 03 2016