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Write n in binary; a(n) = number represented by rightmost block of 1's.
3

%I #11 Dec 18 2015 19:15:14

%S 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 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 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 Write n in binary; a(n) = number represented by rightmost block of 1's.

%e 13 = 1101 so a(13) = 1.

%t 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 Cf. A089309-A089313.

%Y a(2n+1) = A038712(n+1).

%K nonn,base

%O 0,4

%A _N. J. A. Sloane_, Dec 22 2003

%E More terms from _Vladeta Jovovic_, Jan 20 2004