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6 X 6 X 6 triangular graph without horizontal edges coloring a rectangular array: number of n X 1 0..20 arrays where 0..20 label nodes of a graph with edges 0,1 0,2 1,3 1,4 2,4 2,5 3,6 3,7 4,7 4,8 5,8 5,9 6,10 6,11 7,11 7,12 8,12 8,13 9,13 9,14 10,15 10,16 11,16 11,17 12,17 12,18 13,18 13,19 14,19 14,20 and every array movement to a horizontal or vertical neighbor moves along an edge of this graph.
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%I #6 May 27 2021 14:43:11

%S 21,60,190,600,1946,6264,20440,66208,216452,702768,2298936,7470944,

%T 24444168,79466336,260022112,845441152,2766427344,8995380672,

%U 29434608608,95712808320,313191301792,1018418848640,3332470833536,10836405217792

%N 6 X 6 X 6 triangular graph without horizontal edges coloring a rectangular array: number of n X 1 0..20 arrays where 0..20 label nodes of a graph with edges 0,1 0,2 1,3 1,4 2,4 2,5 3,6 3,7 4,7 4,8 5,8 5,9 6,10 6,11 7,11 7,12 8,12 8,13 9,13 9,14 10,15 10,16 11,16 11,17 12,17 12,18 13,18 13,19 14,19 14,20 and every array movement to a horizontal or vertical neighbor moves along an edge of this graph.

%C Column 1 of A223467.

%H R. H. Hardin, <a href="/A223460/b223460.txt">Table of n, a(n) for n = 1..210</a>

%F Empirical: a(n) = 20*a(n-2) -126*a(n-4) +304*a(n-6) -252*a(n-8) +80*a(n-10) -8*a(n-12).

%e Some solutions for n=3

%e ..1...15...11....1...11....6...12....7....4....4....8....9....1....2....7...13

%e ..0...10....7....3...16...11...18...11....8....8....5....5....3....4....4...19

%e ..2...15...11....6...10....6...13....7...12....5....9....9....1....8....2...14

%Y Cf. A223467.

%K nonn

%O 1,1

%A _R. H. Hardin_ Mar 20 2013