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 A023405 #12 Jan 27 2022 22:45:42 %S A023405 4,4,9,4,9,9,4,9,4,9,4,4,9,9,4,9,4,9,9,9,4,4,4,4,9,4,4,4,4,9,9,9,9,4, %T A023405 9,4,4,9,9,4,4,9,9,4,9,4,4,9,4,9,4,9,4,4,4,4,4,4,9,9,9,9,4,9,4,4,4,9, %U A023405 9,4,4,9,4,4,9,9,4,4,9,9,9,4,9,9,9,9,9,9,4,4,9,4,4,9,9,9,9,9,9,4,4,4,9,9,4,4,4,4 %N A023405 If any power of 2 ends with k 4's and 9's, they must be the first k terms of this sequence in reverse order. %H A023405 Ray Chandler, <a href="/A023405/b023405.txt">Table of n, a(n) for n = 1..10000</a> %K A023405 nonn,base %O A023405 1,1 %A A023405 _David W. Wilson_