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 A093403 #25 Jul 08 2021 06:25:19 %S A093403 59,55555559,555555555559,555555555555555559, %T A093403 55555555555555555555555559,55555555555555555555555555555559 %N A093403 Primes of the form 50*R_k + 9, where R_k is the repunit (A002275) of length k. %C A093403 Primes of the form (5*10^k + 31)/9. - _Vincenzo Librandi_, Nov 17 2010 %H A093403 Makoto Kamada, <a href="https://stdkmd.net/nrr/5/55559.htm#prime">Prime numbers of the form 55...559</a>. %H A093403 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a> %F A093403 a(n) = (50*10^A056687(n) + 31)/9 = (5*10^A099418(n) + 31)/9. %Y A093403 Cf. A056687 (corresponding k), A099418. %K A093403 nonn %O A093403 1,1 %A A093403 _Rick L. Shepherd_, Mar 28 2004 %E A093403 Edited by _Ray Chandler_, Feb 27 2012