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 A173021 Number of numbers <= n having in binary representation neither isolated ones nor isolated double ones. 6
 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 9, 9, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,8 COMMENTS a(A173024(n+1)) = a(A173024(n)) + 1; a(2^n - 1)) = A005252(n+1); a(n) <= A173022(n) <= A173023(n). LINKS R. Zumkeller, Table of n, a(n) for n = 0..10000 MATHEMATICA ioQ[n_]:=Module[{idn2=Split[IntegerDigits[n, 2]]}, FreeQ[idn2, {1}]&&FreeQ[ idn2, {1, 1}]]; Accumulate[Table[If[ioQ[n], 1, 0], {n, 0, 90}]] (* Harvey P. Dale, May 15 2016 *) CROSSREFS a(30)=#{0, 7, 14, 15, 28, 30}=#{0, 111, 1110, 1111, 11100, 11110}=6. Sequence in context: A029393 A275150 A303904 * A109703 A103375 A285758 Adjacent sequences:  A173018 A173019 A173020 * A173022 A173023 A173024 KEYWORD base,nonn,look AUTHOR Reinhard Zumkeller, Feb 07 2010 STATUS approved

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Last modified October 20 15:22 EDT 2018. Contains 316388 sequences. (Running on oeis4.)