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 A093941 #14 Jul 08 2021 06:00:56 %S A093941 5,577,577777777,577777777777777,577777777777777777, %T A093941 5777777777777777777,5777777777777777777777777777777777, %U A093941 577777777777777777777777777777777777 %N A093941 Primes of the form 5*10^k + 7*R_k, where R_k is the repunit (A002275) of length k. %H A093941 Makoto Kamada, <a href="https://stdkmd.net/nrr/5/57777.htm#prime">Prime numbers of the form 577...77</a>. %H A093941 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>. %Y A093941 Cf. A002275, A056715 (corresponding k). %K A093941 nonn %O A093941 1,1 %A A093941 _Rick L. Shepherd_, Apr 17 2004