In combinatorial mathematics, Moreau's necklace-counting function

where μ is the classic Möbius function, counts the number of "necklaces" asymmetric under rotations that can be made by arranging n beads the color of each of which is chosen from a list of α colors. One respect in which the word necklace may be misleading is that if one picks such a "necklace" up off the table and turns it over, thus reversing the roles of clockwise and counterclockwise, one gets a different "necklace", counted separately, unless the necklace is symmetric under such reflections.

This function is involved in the cyclotomic identity.

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