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 A089648 #18 Feb 16 2025 08:32:51 %S A089648 0,1,2,4,5,6,9,10,12,17,18,19,20,21,22,24,25,26,28,35,37,38,41,42,44, %T A089648 49,50,52,56,67,69,70,71,73,74,75,76,77,78,81,82,83,84,85,86,88,89,90, %U A089648 92,97,98,99,100,101,102,104,105,106,108,112,113,114,116,120,135,139 %N A089648 Numbers whose numbers of zeros and ones in binary representation differ at most by 1. %C A089648 A031443 is a subsequence; abs(A037861(a(n))) <= 1. %H A089648 Reinhard Zumkeller, <a href="/A089648/b089648.txt">Table of n, a(n) for n = 1..10000</a> %H A089648 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/DigitCount.html">Digit Count</a> %H A089648 <a href="/index/Bi#binary">Index entries for sequences related to binary expansion of n</a> %t A089648 Select[Range[0,7! ],Abs[DigitCount[ #,2,0]-DigitCount[ #,2,1]]<2 &] (* _Vladimir Joseph Stephan Orlovsky_, Feb 16 2010 *) %o A089648 (Haskell) %o A089648 a089648 n = a089648_list !! (n-1) %o A089648 a089648_list = filter ((<= 1) . abs . a037861) [0..] %o A089648 -- _Reinhard Zumkeller_, Mar 31 2015 %Y A089648 Cf. A023416, A000120. %Y A089648 Cf. A037861, union of A031443, A031444 and A031448. %K A089648 nonn,base %O A089648 1,3 %A A089648 _Reinhard Zumkeller_, Jan 02 2004