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A185437 The least number of colors required to color an n-bead necklace so that each bead can be identified. 1
1, 2, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
In other words, the least number of colors in any coloring of the necklace that is not symmetric under any element of the corresponding dihedral group.
LINKS
FORMULA
a(n) = 2 for all n > 5.
G.f.: x*(x^2+1)*(x^3-x-1)/(x-1). [Colin Barker, Oct 26 2012]
EXAMPLE
For n=5, one coloring is ABBCC. Any coloring using two symbols will have two indistinguishable beads.
For n > 5, a coloring is ABAAB...B, where ... is zero or more B's. We can tell the A's apart because one has a B on either side, of the other two one is closer to the single B, and one is closer to the long sequence of B's. Of the B's, one has an A on either side. The remaining B's can be distinguished by counting along the string of B's starting at the end with a singleton A.
CROSSREFS
Cf. A185436.
Sequence in context: A347824 A031283 A293229 * A335660 A210681 A366544
KEYWORD
nonn,easy
AUTHOR
Jack W Grahl, Jan 27 2011
STATUS
approved

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Last modified June 24 21:56 EDT 2024. Contains 373690 sequences. (Running on oeis4.)