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 A091189 #12 Jul 08 2021 06:23:54 %S A091189 2221,222222222222222221, %T A091189 2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222221 %N A091189 Primes of the form 20*R_k + 1, where R_k is the repunit (A002275) of length k. %C A091189 Primes of the form 222...221. %C A091189 The number of 2's in each term is given by the corresponding term of A056660 and so the first term too large to include above is 222...2221 (with 120 2's). %H A091189 Makoto Kamada, <a href="https://stdkmd.net/nrr/2/22221.htm#prime">Prime numbers of the form 22...221</a>. %H A091189 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a> %Y A091189 Cf. A056660 (corresponding k), A084832. %Y A091189 Cf. A051200, A004022, A093176, A093177, A089346. %K A091189 bref,nonn %O A091189 1,1 %A A091189 _Rick L. Shepherd_, Feb 22 2004