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 A093405 #22 Aug 27 2024 02:32:33
%S A093405 89,88888888888889,88888888888888889,
%T A093405 88888888888888888888888888888888889
%N A093405 Primes of the form 80*R_k + 9, where R_k is the repunit (A002275) of length k.
%C A093405 Primes of the form (8*10^k + 1)/9. - _Vincenzo Librandi_, Jul 17 2012
%H A093405 Makoto Kamada, <a href="https://stdkmd.net/nrr/8/88889.htm#prime">Prime numbers of the form 88...889</a>.
%H A093405 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%t A093405 Select[Table[(8*10^n+1)/9,{n,1,200}],PrimeQ] (* _Vincenzo Librandi_, Jul 17 2012 *)
%t A093405 Select[Table[FromDigits[PadLeft[{9},n,8]],{n,100}],PrimeQ] (* _Harvey P. Dale_, Dec 15 2023 *)
%Y A093405 Cf. A056663 (corresponding k).
%K A093405 nonn
%O A093405 1,1
%A A093405 _Rick L. Shepherd_, Mar 28 2004