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 A093139 #11 Jul 08 2021 06:23:50
%S A093139 7,17,1117,11117,11111117,11111111111111111111117,
%T A093139 11111111111111111111111111117,
%U A093139 1111111111111111111111111111111111111117
%N A093139 Primes of the form 10*R_k + 7, where R_k is the repunit (A002275) of length k.
%C A093139 The next term has 131 digits. - _Harvey P. Dale_, Jul 05 2021
%H A093139 Makoto Kamada, <a href="https://stdkmd.net/nrr/1/11117.htm#prime">Prime numbers of the form 11...117</a>.
%H A093139 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>
%t A093139 Select[Table[FromDigits[PadLeft[{7},n,1]],{n,50}],PrimeQ] (* _Harvey P. Dale_, Jul 05 2021 *)
%Y A093139 Cf. A056655 (corresponding k).
%K A093139 nonn
%O A093139 1,1
%A A093139 _Rick L. Shepherd_, Mar 23 2004