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A173589 Integers whose binary representation contains exactly three 1's, no two 1's being adjacent. 1
21, 37, 41, 42, 69, 73, 74, 81, 82, 84, 133, 137, 138, 145, 146, 148, 161, 162, 164, 168, 261, 265, 266, 273, 274, 276, 289, 290, 292, 296, 321, 322, 324, 328, 336, 517, 521, 522, 529, 530, 532, 545, 546, 548, 552, 577, 578, 580, 584, 592, 641, 642, 644, 648 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Subsequence of A014311. [R. J. Mathar, Feb 24 2010]

A000120(a(n))=3; A023416(a(n))>1; 1 < A087116(a(n))<=3. [Reinhard Zumkeller, Mar 11 2010]

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1) = 21 = 10101_2.

a(2) = 37 = 100101_2.

a(3) = 41 = 101001_2.

MAPLE

seq(seq(seq(2^a+2^b+2^c, c=0..b-2), b=2..a-2), a=4..10); # Robert Israel, Dec 19 2016

MATHEMATICA

e31sQ[n_]:=Module[{idn2=IntegerDigits[n, 2]}, Total[idn2]==3 && SequenceCount[ idn2, {1, 1}]==0]; Select[Range[700], e31sQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Sep 20 2018 *)

CROSSREFS

Cf. A000120, A014311, A023416, A087116.

Sequence in context: A168513 A067598 A043683 * A043572 A043728 A043738

Adjacent sequences:  A173586 A173587 A173588 * A173590 A173591 A173592

KEYWORD

base,nonn

AUTHOR

David Koslicki (koslicki(AT)math.psu.edu), Feb 22 2010

EXTENSIONS

More terms from R. J. Mathar, Feb 24 2010

STATUS

approved

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Last modified October 23 00:24 EDT 2020. Contains 337962 sequences. (Running on oeis4.)