A223347 3 X 3 X 3 triangular graph without horizontal edges coloring a rectangular array: number of n X 3 0..5 arrays where 0..5 label nodes of a graph with edges 0,1 0,2 1,3 1,4 2,4 2,5 and every array movement to a horizontal or vertical neighbor moves along an edge of this graph.
28, 236, 2280, 20836, 202264, 1851020, 17970056, 164457412, 1596586328, 14611562156, 141852049992, 1298194798372, 12603142057880, 115340831992268, 1119752515193608, 10247697449986948, 99486754138704856, 910478112673392620
Offset: 1
Keywords
Examples
Some solutions for n=3: ..1..4..1....1..4..2....2..0..2....0..2..4....5..2..0....4..1..0....4..2..5 ..0..2..4....0..2..0....4..1..0....1..4..1....2..5..2....1..4..1....2..5..2 ..1..0..1....2..4..1....2..4..1....0..1..3....0..2..4....4..1..0....4..2..5
Links
- R. H. Hardin, Table of n, a(n) for n = 1..210
Crossrefs
Cf. A223352.
Formula
Empirical: a(n) = 91*a(n-2) - 192*a(n-4) + 64*a(n-6).
Empirical g.f.: 4*x*(7 + 59*x - 67*x^2 - 160*x^3 + 40*x^4 + 64*x^5) / (1 - 91*x^2 + 192*x^4 - 64*x^6). - Colin Barker, Aug 19 2018
Comments