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 A073139 #11 Aug 11 2014 22:45:22
%S A073139 0,0,0,0,0,1,1,0,0,3,3,3,3,3,3,0,0,7,7,9,7,9,9,7,7,9,9,7,9,7,7,0,0,15,
%T A073139 15,21,15,21,21,21,15,21,21,21,21,21,21,15,15,21,21,21,21,21,21,15,21,
%U A073139 21,21,15,21,15,15,0,0,31,31,45,31,45,45,49,31,45,45,49,45,49,49,45,31
%N A073139 Difference between the largest and smallest number having in binary representation the same number of 0's and 1's as n.
%C A073139 a(n) = A073138(n) - A073137(n).
%H A073139 Harvey P. Dale, <a href="/A073139/b073139.txt">Table of n, a(n) for n = 0..1000</a>
%H A073139 <a href="/index/Bi#binary">Index entries for sequences related to binary expansion of n</a>
%t A073139 d[n_]:=Module[{idn2=IntegerDigits[n,2]},FromDigits[Sort[idn2,#1>#2&],2]- FromDigits[ RotateRight[Sort[idn2],1],2]]; Array[d,90,0] (* _Harvey P. Dale_, Oct 22 2011 *)
%Y A073139 Cf. A007088, A073140, A073141.
%K A073139 nonn
%O A073139 0,10
%A A073139 _Reinhard Zumkeller_, Jul 16 2002