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 A053336 #20 Dec 21 2020 07:36:43
%S A053336 6,56,656,6656,66656,566656,6566656,66566656,666566656,6666566656,
%T A053336 56666566656,656666566656,6656666566656,66656666566656,
%U A053336 566656666566656,6566656666566656,56566656666566656,556566656666566656
%N A053336 a(n) contains n digits (either '5' or '6') and is divisible by 2^n.
%H A053336 Ray Chandler, <a href="/A053336/b053336.txt">Table of n, a(n) for n = 1..1000</a>
%F A053336 a(n) = a(n-1)+10^(n-1)*(6-[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 5.
%F A053336 Conjecture: a(n) = 10^n - A035014(n). - _J. Lowell_, Nov 16 2020
%t A053336 Block[{a = {6}, k, m, w}, Do[k = 1; If[Mod[a[[-1]], 2^i] == 0, Set[w, Prepend[ConstantArray[5, i - 1], 6]], Set[w, ConstantArray[5, i]]]; While[Mod[Set[m, FromDigits[w + PadLeft[IntegerDigits[k, 2], i]]], 2^i] != 0, k++]; AppendTo[a, m], {i, 2, 18}]; a] (* _Michael De Vlieger_, Dec 10 2020 *)
%Y A053336 Cf. A023408, A050621, A050622, A035014.
%K A053336 base,nonn
%O A053336 1,1
%A A053336 _Henry Bottomley_, Mar 06 2000