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A350715
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2-tone chromatic number of a wheel graph with n vertices.
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3
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8, 8, 7, 7, 8, 7, 7, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 10, 10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 11, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 15, 15, 15, 15, 15
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OFFSET
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4,1
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COMMENTS
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The 2-tone chromatic number of a graph G is the smallest number of colors for which G has a coloring where every vertex has two distinct colors, no adjacent vertices have a common color, and no pair of vertices at distance 2 have two common colors.
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LINKS
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FORMULA
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a(n) = ceiling((5 + sqrt(8*n - 7))/2) for n > 11.
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EXAMPLE
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The central vertex always requires two distinct colors. All vertices on the cycle require distinct pairs.
The colorings for small (broken) cycles are shown below.
-12-34-56-
-12-34-15-36-
-12-34-51-23-45-
-12-34-15-32-14-35-
-12-34-56-13-24-35-46-
-12-34-15-23-14-25-13-45-
-12-34-15-32-14-25-13-24-35-
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MATHEMATICA
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A350715[n_]:=If[n<12, {8, 8, 7, 7, 8, 7, 7, 8}[[n-3]], Ceiling[(5+Sqrt[8n-7])/2]]; Array[A350715, 100, 4] (* Paolo Xausa, Nov 30 2023 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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