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 A223240 3-loop graph coloring a rectangular array: number of n X 1 0..6 arrays where 0..6 label nodes of a graph with edges 0,1 1,2 2,0 0,3 3,4 4,0 0,5 5,6 6,0 and every array movement to a horizontal or vertical neighbor moves along an edge of this graph. 1
 7, 18, 60, 168, 528, 1536, 4704, 13920, 42144, 125664, 378528, 1132512, 3403680, 10198752, 30620832, 91813344, 275538336, 826418400, 2479648416, 7438158816, 22316049312, 66945002208, 200841298080, 602511311328, 1807559099808 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Column 1 of A223247. LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = a(n-1) + 6*a(n-2). Conjectures from Colin Barker, Aug 17 2018: (Start) G.f.: x*(7 + 11*x) / ((1 + 2*x)*(1 - 3*x)). a(n) = (64*3^n - 9*(-2)^n) / 30. (End) EXAMPLE Some solutions for n=3: ..0....5....6....0....4....3....1....1....0....1....6....0....2....0....1....5 ..1....6....0....3....0....0....2....0....5....0....0....4....1....2....0....0 ..0....5....4....0....4....2....1....1....6....5....2....0....2....0....4....5 CROSSREFS Cf. A223247. Sequence in context: A220031 A197092 A288743 * A304142 A019534 A024830 Adjacent sequences: A223237 A223238 A223239 * A223241 A223242 A223243 KEYWORD nonn AUTHOR R. H. Hardin, Mar 18 2013 STATUS approved

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Last modified September 7 09:14 EDT 2024. Contains 375730 sequences. (Running on oeis4.)