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A223337
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.
1
15, 60, 264, 1176, 5280, 23712, 106560, 478848, 2151936, 9670656, 43459584, 195305472, 877694976, 3944325120, 17725636608, 79658287104, 357981093888, 1608752431104, 7229667803136, 32489832185856, 146007980507136
OFFSET
1,1
COMMENTS
Column 1 of A223344.
LINKS
FORMULA
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
EXAMPLE
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
CROSSREFS
Cf. A223344.
Sequence in context: A206238 A064761 A005945 * A110755 A206231 A001756
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 19 2013
STATUS
approved