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 A177504 #13 Sep 08 2022 08:45:53
%S A177504 41,491,49991,49999991,4999999999999999999999991
%N A177504 Primes of the form 5*10^n-9.
%H A177504 Vincenzo Librandi, <a href="/A177504/b177504.txt">Table of n, a(n) for n = 1..9</a>
%t A177504 Select[Table[5 10^n - 9, {n, 250}], PrimeQ] (* _Vincenzo Librandi_, Jan 03 2014 *)
%o A177504 (Magma)[a: n in [0..250] | IsPrime(a) where a is 5*10^n-9];
%Y A177504 Cf. A086949, A103001.
%K A177504 nonn
%O A177504 1,1
%A A177504 _Vincenzo Librandi_, Dec 11 2010