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COUNTING SYMMETRIC BRACELETS

Part of: Combinatorics Graph theory Elementary number theory

Published online by Cambridge University Press:  22 August 2013

YEVHEN ZELENYUK  and
YULIYA ZELENYUK
YEVHEN ZELENYUK*
Affiliation:
School of Mathematics, University of the Witwatersrand, Private Bag 3, Wits, 2050, Johannesburg, South Africa email [email protected]
YULIYA ZELENYUK
Affiliation:
School of Mathematics, University of the Witwatersrand, Private Bag 3, Wits, 2050, Johannesburg, South Africa email [email protected]
*
✉[email protected]
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Abstract

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An $r$-ary necklace (bracelet) of length $n$ is an equivalence class of $r$-colourings of vertices of a regular $n$-gon, taking all rotations (rotations and reflections) as equivalent. A necklace (bracelet) is symmetric if a corresponding colouring is invariant under some reflection. We show that the number of symmetric $r$-ary necklaces (bracelets) of length $n$ is $\frac{1}{2} (r+ 1){r}^{n/ 2} $ if $n$ is even, and ${r}^{(n+ 1)/ 2} $ if $n$ is odd.

Keywords

necklacebraceletsymmetrycolouringfinite cyclic groupdihedral group

MSC classification

Secondary: 05A15: Exact enumeration problems, generating functions 05C15: Coloring of graphs and hypergraphs 05C25: Graphs and abstract algebra (groups, rings, fields, etc.) 11A25: Arithmetic functions; related numbers; inversion formulas
Type
Research Article
Information
Bulletin of the Australian Mathematical Society , Volume 89 , Issue 3 , June 2014 , pp. 431 - 436
Copyright
Copyright ©2013 Australian Mathematical Publishing Association Inc. 

References

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