A223212 3X3X3 triangular graph coloring a rectangular array: number of nX2 0..5 arrays where 0..5 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 and every array movement to a horizontal or vertical neighbor moves along an edge of this graph

18, 126, 918, 6642, 48114, 348462, 2523798, 18278946, 132387858, 958837662, 6944516694, 50296639122, 364280484978, 2638352661966, 19108640336598, 138397015977282, 1002359858893074, 7259732297153982, 52579632512961558

Offset

1,1

Comments

Column 2 of A223218

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = 6*a(n-1) +9*a(n-2).

Empirical g.f.: -18*x*(1+x)/(-1+6*x+9*x^2) . a(n) = 18*(A189801(n)+A189801(n-1)). - R. J. Mathar, May 21 2018

Example

Some solutions for n=3
..0..1....1..4....0..1....0..2....4..1....4..1....4..2....2..4....0..2....5..2
..2..4....2..1....1..0....1..4....1..2....2..4....2..4....4..1....2..0....2..5
..0..2....1..2....4..1....3..1....4..1....4..2....0..2....1..2....0..1....0..2

Crossrefs

Sequence in context: A101378 A107417 A056125 * A297027 A027566 A335781

Adjacent sequences: A223209 A223210 A223211 * A223213 A223214 A223215

Keyword

nonn

Author

R. H. Hardin Mar 18 2013

Status

approved