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 A174205 #18 Mar 23 2020 17:31:34 %S A174205 1,0,1,0,1,1,0,1,1,0,1,0,1,0,1,0,1,1,0,1,1,1,0,1,1,0,0,1,0,1,0,0,1,0, %T A174205 1,1,0,0,1,1,0,1,0,1,1,1,0,1,0,1,0,1,1,0,1,1,0,1,1,1,1,0,1,1,1,0,0,1, %U A174205 0,0,1,0,0,1,0,0,1,0,1,0,0,1,1,0,1,0,0,1,1,1,0,0,1,0,1,0,1,0,1,0,1,1,0,1,0,1,1,0,1,1,0,1,1,1,0,0,1,0,1,0,1,0,1,0,1,1,0,1,0,1,1,0,1 %N A174205 Write natural numbers in base 2 as a stream of digits. Moving left to right, delete odd occurrences of digit 0 and 1. %C A174205 The natural numbers in base 2 are 0, 1, 10, 11, 100, 101, 110, 111, 1000..... and define a stream of digits if concatenated: %C A174205 0110111001011101111000 Delete odd-indexed occurrences of 0 (replaced by .): %C A174205 .110111.01.11101111.0. Also delete odd-indexed occurrences of 1 (replaced by .): %C A174205 ..10.1..01..1.01.1..0. %C A174205 The stream of bits that remain after these two rounds of deletion is chopped into single bits which define the entries of the current sequence. %o A174205 (Sage) %o A174205 def A174205(N=100): %o A174205 a = [0] + flatten([n.digits(base=2)[::-1] for n in IntegerRange(1,N)]) %o A174205 for bit in 0, 1: %o A174205 a = [d for i,d in enumerate(a) if not (d == bit and a[:i+1].count(bit) % 2 == 1)] %o A174205 return a # _D. S. McNeil_, Dec 08 2010 %Y A174205 Cf. A007088, A174203 - A174210. %K A174205 easy,nonn,base %O A174205 1,1 %A A174205 _Paolo P. Lava_ and _Giorgio Balzarotti_, Mar 15 2010