A273494 a(n) = A245325(n) + A245326(n).

2, 3, 3, 5, 4, 5, 4, 8, 7, 7, 5, 8, 7, 7, 5, 13, 11, 12, 9, 11, 10, 9, 6, 13, 11, 12, 9, 11, 10, 9, 6, 21, 18, 19, 14, 19, 17, 16, 11, 18, 15, 17, 13, 14, 13, 11, 7, 21, 18, 19, 14, 19, 17, 16, 11, 18, 15, 17, 13, 14, 13, 11, 7, 34, 29, 31, 23, 30, 27, 25, 17, 31, 26, 29, 22, 25, 23, 20, 13, 29, 25, 26, 19, 27, 24, 23, 16, 23

Offset

1,1

Comments

The terms (n>0) may be written as a left-justified array with rows of length 2^m, m >= 0:

2,

3, 3,

5, 4, 5, 4,

8, 7, 7, 5, 8, 7, 7, 5,

13,11,12, 9,11,10, 9, 6,13,11,12, 9,11,10, 9, 6,

21,18,19,14,19,17,16,11,18,15,17,13,14,13,11, 7,21,18,19,14,19,17,...

All columns have the Fibonacci sequence property: a(2^(m+2) + k) = a(2^(m+1) + k) + a(2^m + k), m >= 0, 0 <= k < 2^m (empirical observations).

The terms (n>0) may also be written as a right-justified array with rows of length 2^m, m >= 0:

2,

3, 3,

5, 4, 5, 4,

8, 7, 7, 5, 8, 7, 7, 5,

13,11,12, 9,11,10, 9, 6,13,11,12, 9,11,10, 9, 6,

..., 18,15,17,13,14,13,11, 7,21,18,19,14,19,17,16,11,18,15,17,13,14,13,11, 7,

Each column is an arithmetic sequence. The differences of the arithmetic sequences give the sequence A071585: a(2^(m+1)-1-k) - a(2^m-1-k) = A071585(k), m >= 0, 0 <= k < 2^m.

n > 1 occurs in this sequence phi(n) = A000010(n) times, as it occurs in A007306 (Franklin T. Adams-Watters's comment), which is the sequence obtained by adding numerator and denominator in the Calkin-Wilf enumeration system of positive rationals. A245325(n)/A245326(n) is also an enumeration system of all positive rationals, and in each level m >= 0 (ranks between 2^m and 2^(m+1)-1) rationals are the same in both systems. Thus a(n) has the same terms in each level as A007306.

The same property occurs in all numerator+denominator sequences of enumeration systems of positive rationals, as, for example, A007306 (A007305+A047679), A071585 (A229742+A071766), A086592 (A020650+A020651), A268087 (A162909+A162910).

Links

Yosu Yurramendi, Table of n, a(n) for n = 1..4095

Formula

a(n) = A273493(A059893(n)), a(A059893(n)) = A273493(n), n > 0. - Yosu Yurramendi, May 30 2017

a(n) = A007306(A059893(A180200(n))) = A007306(A059894(A154435(n))). - Yosu Yurramendi, Sep 20 2021

Prog

(PARI) a(n) = my(x=1, y=1); for(i=0, logint(n, 2), if(bittest(n, i), [x, y]=[x+y, y], [x, y]=[y, x+y])); x \\ Mikhail Kurkov, Mar 10 2023

Crossrefs

Cf. A007306, A268087, A071585, A086592, A273493

Sequence in context: A210874 A244796 A080391 * A116922 A086898 A123031

Adjacent sequences: A273491 A273492 A273493 * A273495 A273496 A273497

Keyword

nonn

Author

Yosu Yurramendi, May 23 2016

Status

approved