

A162911


Numerators of drib tree fractions, where drib is the bitreversal permutation tree of the Bird tree.


3



1, 1, 2, 2, 3, 1, 3, 3, 5, 1, 4, 3, 4, 2, 5, 5, 8, 2, 7, 4, 5, 3, 7, 4, 7, 1, 5, 5, 7, 3, 8, 8, 13, 3, 11, 7, 9, 5, 12, 5, 9, 1, 6, 7, 10, 4, 11, 7, 11, 3, 10, 5, 6, 4, 9, 7, 12, 2, 9, 8, 11, 5, 13, 13, 21, 5, 18, 11, 14, 8, 19, 9, 16, 2, 11, 12, 17, 7, 19, 9, 14, 4, 13, 6, 7, 5, 11, 10, 17, 3, 13
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OFFSET

1,3


COMMENTS

The drib tree is an infinite binary tree labelled with rational numbers. It is generated by the following iterative process: start with the rational 1; for the left subtree increment and then reciprocalise the current rational; for the right subtree interchange the order of the two steps: the rational is first reciprocalised and then incremented. Like the SternBrocot and the Bird tree, the drib tree enumerates all the positive rationals (A162911(n)/A162912(n)).


REFERENCES

R. Hinze, Functional pearls: the bird tree, J. Funct. Programming 19 (2009), no. 5, 491508.


LINKS

Table of n, a(n) for n=1..91.


FORMULA

a(n) where a(1) = 1; a(2n) = b(n); a(2n+1) = a(n) + b(n); and b(1) = 1; b(2n) = a(n) + b(n); b(2n+1) = a(n);


EXAMPLE

The first four levels of the drib tree: [1/1] [1/2, 2/1] [2/3, 3/1, 1/3, 3/2], [3/5, 5/2, 1/4, 4/3, 3/4, 4/1, 2/5, 5/3]


PROG

(Other) import Ratio; drib :: [Rational]; drib = 1 : map (recip . succ) drib \/ map (succ . recip) drib; (a : as) \/ bs = a : (bs \/ as); a162911 = map numerator drib; a162912 = map denominator drib


CROSSREFS

This sequence is the composition of A162909 and A059893: a(n) = A162909(A059893(n)). This sequence is a permutation of A002487(n+1).
Sequence in context: A224764 A077268 A088741 * A131821 A204123 A237448
Adjacent sequences: A162908 A162909 A162910 * A162912 A162913 A162914


KEYWORD

easy,frac,nonn


AUTHOR

Ralf Hinze (ralf.hinze(AT)comlab.ox.ac.uk), Aug 05 2009


STATUS

approved



