A173589 Integers whose binary representation contains exactly three 1's, no two 1's being adjacent.

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

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