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 A248349 #24 Sep 08 2022 08:46:10 %S A248349 4,11,17,23,26,79,82,221,526,821,1204,5392,13139,35879,60991,77669 %N A248349 Numbers k such that 10^k + 123456789 is prime. %C A248349 a(14) > 20000. %C A248349 a(17) > 2*10^5. - _Robert Price_, Oct 26 2019 %t A248349 Select[Range[10^4], PrimeQ[10^# + 123456789] &] (* _Robert Price_, Sep 08 2019 *) %o A248349 (PARI) for(n=1,10^4,if(ispseudoprime(10^n + 123456789),print1(n,", "))) %o A248349 (Magma) [n: n in [1..500] | IsPrime(10^n + 123456789)]; // _Vincenzo Librandi_, Oct 12 2014 %Y A248349 Cf. A248350, A248351, A248352, A050289. %K A248349 nonn,more,hard %O A248349 1,1 %A A248349 _Derek Orr_, Oct 05 2014 %E A248349 a(14)-a(16) from _Robert Price_, Oct 26 2019