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 A072629 #22 Feb 09 2019 23:25:10 %S A072629 0,0,1,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0, %T A072629 1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, %U A072629 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 %N A072629 Parity of n*floor(log n). %C A072629 a(n)=1 for n: 3, 5, 7, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 149, 151, .... - _Robert G. Wilson v_, Feb 01 2015 %H A072629 Antti Karttunen, <a href="/A072629/b072629.txt">Table of n, a(n) for n = 1..100000</a> %H A072629 <a href="/index/Ch#char_fns">Index entries for characteristic functions</a> %F A072629 a(n) = n*floor(log(n)) mod 2. %e A072629 Parity either alternates or it is steadily 0. Intervals of such kind also change and return: 01010...0000....0101.., etc. %t A072629 f[n_] := Mod[n*Floor@ Log@ n, 2]; Array[f, 105] (* _Robert G. Wilson v_, Feb 01 2015 *) %o A072629 (PARI) a(n) = (log(n)\1*n)%2; \\ _Charles R Greathouse IV_, Sep 04 2015, corrected by _Antti Karttunen_, Feb 06 2019 %Y A072629 Cf. A004648, A072608, A072609, A072610, A072630. %K A072629 nonn %O A072629 1,1 %A A072629 _Labos Elemer_, Jun 28 2002