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 A174204 #9 Aug 24 2012 10:50:03 %S A174204 0,1,1,2,1,1,1,4,1,2,1,2,5,1,3,4,1,1,1,4,5,2,3,4,5,2,3,6,5,3,3,8 %N A174204 Scan the sequence of natural numbers, written in base 2, from left to right, delete each 2nd, 4th, 6th etc occurrence of digit 0 and each 2nd, 4th, 6th etc occurrence of digit 1. The sequence are the base-10 residuals. %C A174204 Deleting the even occurrences of 0 and the odd occurrences of 1, we get the same sequence apart from the initial three terms 0,1,1 replaced by 0. %e A174204 Numbers in base 2 (A007088): %e A174204 0, 1, 10, 11, 100, 101, 110, 111, 1000..... %e A174204 Delete 2nd, 4th, 6th,.. (even) occurrence of 0 (replaced by ~): %e A174204 0, 1, 1~, 11, 10~, 101, 11~, 111, 10~0 %e A174204 Delete 2nd, 4th 6th,... (even) occurrence of 1 (replaced by ~): %e A174204 0, 1, ~~, 1~, 10~, ~01, ~1~, ~1~, 10~0 %e A174204 The numbers left are: %e A174204 0, 1, 1, 10, 1, 1, 1, 100, and in base 10: 0, 1, 1, 2, 1, 1, 1, 4, ....as shown by a(n). %Y A174204 Cf. A174203, A174205-A174210. %K A174204 easy,nonn,base,less %O A174204 0,4 %A A174204 _Paolo P. Lava_ and _Giorgio Balzarotti_, Mar 15 2010