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 A175949 #5 Mar 31 2012 20:25:48
%S A175949 1,2,3,6,5,4,7,14,13,10,11,12,9,8,15,30,29,26,27,18,21,20,23,28,25,22,
%T A175949 19,24,17,16,31,62,61,58,59,50,53,52,55,34,37,42,43,36,41,40,47,60,57,
%U A175949 54,51,38,45,44,39,56,49,46,35,48,33,32,63,126,125,122,123,114,117,116
%N A175949 Numbers obtained by concatenation of the binary representation of A175946(n) and A175945(n).
%C A175949 The operation as in A175948, but the run-length encoding of zeros (A175946) is placed left from the run-length encoding of ones (A175945).
%e A175949 n=9 is 1001 in binary. Run lengths of 0's are 2 (one run of length 2) and of 1's are 11 (two runs each of length 1). The concatenation of these lengths is 211, which is interpreted as 2 one's, 1 zero, 1 one, binary 1101, and recoded decimal as a(9)=8+4+1 =13.
%t A175949 takelist[l_, t_] := Module[{lent, term},Set[lent, Length[t]]; Table[l[[t[[y]]]], {y, 1, lent}]]
%t A175949 frombinrep[x_] := FromDigits[Flatten[Table[Table[If[OddQ[n], 1, 0], {d, 1, x[[n]]}], {n, 1, Length[x]}]], 2]
%t A175949 binrep[x_] := repcount[IntegerDigits[x, 2]]
%t A175949 onebinrep[x_]:=Module[{b},b=binrep[x];takelist[b,Range[1,Length[b],2]]]
%t A175949 zerobinrep[x_]:=Module[{b},b=binrep[x];takelist[b,Range[2,Length[b],2]]]
%t A175949 Table[frombinrep[Flatten[{zerobinrep[n], onebinrep[n]}]], {n,START,END}]
%K A175949 base,nonn
%O A175949 1,2
%A A175949 _Dylan Hamilton_, Oct 28 2010