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 A053335 #5 Jun 13 2020 15:02:49 %S A053335 6,36,336,6336,66336,366336,6366336,36366336,636366336,3636366336, %T A053335 33636366336,333636366336,3333636366336,33333636366336, %U A053335 633333636366336,3633333636366336,33633333636366336,333633333636366336 %N A053335 a(n) contains n digits (either '3' or '6') and is divisible by 2^n. %H A053335 Ray Chandler, <a href="/A053335/b053335.txt">Table of n, a(n) for n = 1..1000</a> %F A053335 a(n)=a(n-1)+10^(n-1)*(6-3*[a(n-1)/2^(n-1) mod 2]) i.e. a(n) ends with a(n-1); if (n-1)-th term is divisible by 2^n then n-th term begins with a 6, if not then n-th term begins with a 3. %Y A053335 Cf. A023407, A050621, A050622, A035014. %K A053335 base,nonn %O A053335 1,1 %A A053335 _Henry Bottomley_, Mar 06 2000