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 A033666 #20 Apr 14 2021 12:00:34
%S A033666 1,1,1,2,1,2,2,3,1,3,2,4,2,4,3,5,1,2,3,4,2,3,4,5,2,3,4,5,3,4,5,6,1,3,
%T A033666 2,4,3,5,4,6,2,4,3,5,4,6,5,7,2,4,3,5,4,6,5,7,3,5,4,6,5,7,6,8,1,3,3,5,
%U A033666 2,4,4,6,3,5,5,7,4,6,6,8,2,4,4,6,3,5,5,7,4,6,6,8,5,7,7,9,2,4,4,6,3,5
%N A033666 Base-2 digital convolution sequence (with smallest digits).
%H A033666 Alois P. Heinz, <a href="/A033666/b033666.txt">Table of n, a(n) for n = 0..20000</a>
%H A033666 Michael Gilleland, <a href="/selfsimilar.html">Some Self-Similar Integer Sequences</a>
%p A033666 a:= proc(n) option remember; `if`(n=0, 1, (l->
%p A033666 add(l[-i]*a(i-1), i=1..nops(l)))(Bits[Split](n)))
%p A033666 end:
%p A033666 seq(a(n), n=0..101); # _Alois P. Heinz_, Apr 14 2021
%t A033666 c[ 0, _ ] := 1; c[ n_, b_ ] := c[ n, b ]=Module[ {mul}, mul=IntegerDigits[ n, b ]; Table[ c[ i, b ], {i, 0, Length[ mul ]-1} ].mul ]
%K A033666 nonn,base
%O A033666 0,4
%A A033666 _David W. Wilson_, _Wouter Meeussen_