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 A066879 #15 Feb 11 2014 19:05:25 %S A066879 4,5,18,19,20,21,24,25,70,71,74,75,76,77,82,83,84,85,88,89,98,99,100, %T A066879 101,104,105,112,113,270,271,278,279,282,283,284,285,294,295,298,299, %U A066879 300,301,306,307,308,309,312,313,326,327,330,331,332,333,338,339,340 %N A066879 n such that there are as many 1's as 0's in the base 2 expansion of Floor(n/2). %C A066879 n such that there are as many odd as even terms in the orbit f(n), f(f(n)), f(f(f(n))), ..., 1, where f(k) = Floor(k/2). %F A066879 A037861(Floor(n/2)) = 0. %e A066879 floor(18/2) = 9 = 1001 (base 2) has the same number of 1's as 0's. So 18 is a term of the sequence. %e A066879 Also the orbit corresponding to 18 is 9, 4, 2, 1, which has an equal number (i.e. 2) of odd and even terms. %t A066879 Select[Range[500],DigitCount[Floor[#/2],2,1]==DigitCount[Floor[#/2],2,0]&] (* _Harvey P. Dale_, Jan 14 2014 *) %Y A066879 Complement is the union of 1 and A126388. %K A066879 easy,nonn %O A066879 1,1 %A A066879 _Joseph L. Pe_, Jan 21 2002 %E A066879 Extended and edited by _John W. Layman_, Jan 30 2002 %E A066879 New definition by _Jonathan Sondow_, Jun 10 2011