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 A103091 #19 Jan 17 2019 13:44:07
%S A103091 1,3,6,31,36,61,117,229,339,3165,3958,5277,5343,6079,6535,8485,15084,
%T A103091 34537
%N A103091 Numbers n such that 8*10^n + 7*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
%C A103091 Also numbers n such that (79*10^n+11)/9 is prime.
%C A103091 a(19) > 10^5. - _Robert Price_, Oct 27 2015
%H A103091 Makoto Kamada, <a href="https://stdkmd.net/nrr/8/87779.htm#prime">Prime numbers of the form 877...779</a>.
%H A103091 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A103091 a(n) = A101078(n) + 1.
%t A103091 Do[ If[ PrimeQ[(79*10^n + 11)/9], Print[n]], {n, 0, 10000}]
%Y A103091 Cf. A002275, A101078.
%K A103091 more,nonn
%O A103091 1,2
%A A103091 _Robert G. Wilson v_, Jan 19 2005
%E A103091 a(17) from Kamada data by _Robert Price_, Dec 14 2010
%E A103091 a(18) from Erik Branger May 01 2013 by _Ray Chandler_, Aug 16 2013