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 A093177 #19 Jul 08 2021 06:24:19 %S A093177 991,99991,9999991,999999999999999999999999999999991, %T A093177 999999999999999999999999999999999999999999991, %U A093177 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999991 %N A093177 Primes of the form 90*R_k + 1, where R_k is the repunit (A002275) of length k. %C A093177 Primes of the form 10^k - 9 (k=3,5,7,...). - _Vincenzo Librandi_, Nov 16 2010 %H A093177 Makoto Kamada, <a href="https://stdkmd.net/nrr/9/99991.htm#prime">Prime numbers of the form 99...991</a>. %H A093177 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a> %F A093177 a(n) = 10^(A056696(n)+1) - 9 = 10^A095714(n) - 9. %Y A093177 Cf. A056696 (corresponding k), A095714. %K A093177 nonn %O A093177 1,1 %A A093177 _Rick L. Shepherd_, Mar 27 2004 %E A093177 Edited by _Ray Chandler_, Feb 26 2012