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A223337
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5 X 5 X 5 triangular graph coloring a rectangular array: number of n X 1 0..14 arrays where 0..14 label nodes of a graph with edges 0,1 0,2 1,2 1,3 1,4 2,4 3,4 2,5 4,5 3,6 3,7 4,7 6,7 4,8 5,8 7,8 5,9 8,9 6,10 6,11 7,11 10,11 7,12 8,12 11,12 11,12 8,13 9,13 12,13 9,14 13,14 and every array movement to a horizontal or vertical neighbor moves along an edge of this graph.
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1
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15, 60, 264, 1176, 5280, 23712, 106560, 478848, 2151936, 9670656, 43459584, 195305472, 877694976, 3944325120, 17725636608, 79658287104, 357981093888, 1608752431104, 7229667803136, 32489832185856, 146007980507136
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 4*a(n-1) + 4*a(n-2) - 8*a(n-3).
Empirical g.f.: 3*x*(5 - 12*x^2) / (1 - 4*x - 4*x^2 + 8*x^3). - Colin Barker, Aug 19 2018
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EXAMPLE
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Some solutions for n=3:
..3...11...11....9....4...11....4....5...10....6....8....7....2....8....4....8
..7....7...10....8....7....7....5....8....6....7....4....4....4....9....2...12
..3....8....6....7....3....6....8...12....3....6....7....7....7....5....5...11
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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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