|
|
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
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|