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 A023404 #13 Jan 27 2022 22:45:33 %S A023404 4,4,7,7,4,4,4,4,4,4,7,4,4,4,4,7,7,4,7,7,7,4,7,4,4,7,4,7,4,4,7,7,4,4, %T A023404 7,4,7,7,4,4,4,4,4,4,7,4,7,4,4,4,4,4,7,4,7,4,4,7,7,4,4,4,7,4,7,7,4,4, %U A023404 4,7,7,4,7,4,4,7,4,7,7,7,7,7,4,7,7,7,7,7,7,7,4,4,4,4,4,7,4,7,4,7,7,4,7,7,7,4,4,4 %N A023404 If any power of 2 ends with k 4's and 7's, they must be the first k terms of this sequence in reverse order. %H A023404 Ray Chandler, <a href="/A023404/b023404.txt">Table of n, a(n) for n = 1..10000</a> %K A023404 nonn,base %O A023404 1,1 %A A023404 _David W. Wilson_