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A166736
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Consider triangles stacked so the k-th row has 2*k-1 triangles. a(n) is the number of ways to color each triangle in the first n rows using three colors with the restriction that adjacent triangles must be different colors. (Triangles are adjacent if they share a side.)
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0
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OFFSET
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1,1
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LINKS
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EXAMPLE
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Illustration of first two rows:
/\
/ \
/ 1 \
/ \
/________\
/\ /\
/ \ / \
/ 2 \ 3 / 4 \
/ \ / \
/________\/________\
Triangles sharing a side are considered adjacent; e.g., 1 & 3 are adjacent in the figure, 1 & 2 are not.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Chris Cole (chris(AT)questrel.com), Oct 20 2009
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EXTENSIONS
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STATUS
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approved
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