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 A089312 #11 Dec 18 2015 19:15:14
%S A089312 0,1,1,3,1,1,3,7,1,1,1,3,3,1,7,15,1,1,1,3,1,1,3,7,3,1,1,3,7,1,15,31,1,
%T A089312 1,1,3,1,1,3,7,1,1,1,3,3,1,7,15,3,1,1,3,1,1,3,7,7,1,1,3,15,1,31,63,1,
%U A089312 1,1,3,1,1,3,7,1,1,1,3,3,1,7,15,1,1,1,3,1,1,3,7,3,1,1,3,7,1,15,31,3,1,1,3,1
%N A089312 Write n in binary; a(n) = number represented by rightmost block of 1's.
%e A089312 13 = 1101 so a(13) = 1.
%t A089312 rb1[n_]:=Module[{id=Split[IntegerDigits[n,2]]},If[MemberQ[ Last[ id],0], FromDigits[ id[[-2]],2], FromDigits[id[[-1]],2]]]; Join[{0}, Array[ rb1,100]] (* _Harvey P. Dale_, Dec 18 2015 *)
%Y A089312 Cf. A089309-A089313.
%Y A089312 a(2n+1) = A038712(n+1).
%K A089312 nonn,base
%O A089312 0,4
%A A089312 _N. J. A. Sloane_, Dec 22 2003
%E A089312 More terms from _Vladeta Jovovic_, Jan 20 2004