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 A105431 #13 Jan 17 2019 13:44:08
%S A105431 3,13,113,1113,111113,1111111113,111111111113,
%T A105431 1111111111111111111111113,
%U A105431 1111111111111111111111111111111111111111111111111111111111111111111111111111111111113
%N A105431 Primes of form R_n + 2 {= (10^n + 17)/9}, R_n being the n-th repunit, i.e., primes consisting of a string of 1's followed by a terminal 3.
%C A105431 For the associated positive values n see A097683.
%H A105431 Makoto Kamada, <a href="https://stdkmd.net/nrr/1/11113.htm#prime">Prime numbers of the form 11...113</a>.
%H A105431 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%Y A105431 Cf. A098406.
%K A105431 nonn
%O A105431 1,1
%A A105431 _Lekraj Beedassy_, Apr 08 2005