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 A175096 #7 Mar 11 2014 01:32:50 %S A175096 1,2,1,2,1,2,1,2,1,2,2,2,2,2,1,2,1,4,2,4,1,4,2,2,2,4,1,2,2,2,1,2,1,4, %T A175096 2,2,2,8,2,4,2,2,3,8,3,4,2,2,2,8,1,8,3,2,2,2,2,4,2,2,2,2,1,2,1,4,2,4, %U A175096 2,8,2,4,1,6,6,4,6,8,2,4,2,6,6,6,1,6,3,8,6,6,3,8,3,4,2,2,2,8,1,4,6,4,2,8,6 %N A175096 Write n in binary (without leading 0's). a(n) = the number of distinct numerical values made by permutating the runs of 0's and the runs of 1's, such that the runs (of nonzero length) of 1's alternate with the runs (of nonzero length) of 0's. The permutated binary numbers (those not equal to n) may start with leading 0's. %C A175096 Each "run" of binary digit b (0 or 1) is bounded by digits equal to 1-b, or is bounded by the edge of the binary string (which is n written in binary). %C A175096 For all odd n, the values of all permutations of binary n are themselves odd, since there are an odd number of runs (the first and last runs being of 1's). %e A175096 20 in binary is 10100. So we have a run of one 1, followed by a run of one 0, followed by a run of one 1, followed finally by a run of two 0's. The permutations of the runs of 0's and the run's of 1's form these distinct binary numbers: 00101 (5 in decimal), 01001 (9 in decimal), 10010 (18 in decimal), and 10100 (20 in decimal). So a(20) = 4 since there are 4 such permutations. %K A175096 base,nonn %O A175096 1,2 %A A175096 _Leroy Quet_, Feb 01 2010 %E A175096 Extended by _Ray Chandler_, Feb 07 2010