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 A084474 #7 Mar 31 2017 21:40:18
%S A084474 1,10000,11,100000000,100001,110000,111,1000000000000,1000000001,
%T A084474 1000010000,1000011,1100000000,1100001,1110000,1111,10000000000000000,
%U A084474 10000000000001,10000000010000,10000000011,10000100000000
%N A084474 Write n in binary and replace 0 with 0000.
%C A084474 a(n)=A007088(A084473(n)); in A084472: replace 0 with 00.
%t A084474 Table[FromDigits[Flatten[IntegerDigits[n,2]/.{0->{0,0,0,0}}]],{n,20}] (* _Harvey P. Dale_, Feb 19 2013 *)
%K A084474 nonn
%O A084474 1,2
%A A084474 _Reinhard Zumkeller_, May 27 2003