A198900 Number of n X 2 0..4 arrays with values 0..4 introduced in row major order and no element equal to any horizontal or vertical neighbor.

1, 4, 33, 380, 4801, 62004, 804833, 10459180, 135958401, 1767426404, 22976444833, 298693487580, 3883014452801, 50479185229204, 656229400008033, 8530982176189580, 110902768218720001, 1441735986628126404

Offset: 1

Author

R. H. Hardin, Oct 31 2011

Keywords

• nonn

Comments

Column 2 of A198906.

Examples

			Some solutions with values 0 to 4 for n=4:
..0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1
..2..3....2..3....2..0....1..2....1..0....2..3....2..3....2..3....1..2....2..3
..4..2....1..4....3..2....3..1....2..3....1..4....3..1....4..2....2..3....4..0
..2..4....3..2....4..3....2..4....4..2....4..3....4..2....2..0....4..0....0..3
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..200

Formula

Empirical: a(n) = 17*a(n-1) -55*a(n-2) +39*a(n-3).

Conjectures from Colin Barker, Feb 18 2018: (Start)

G.f.: x*(1 - 13*x + 20*x^2) / ((1 - x)*(1 - 3*x)*(1 - 13*x)).

a(n) = (26 + 13*3^n + 13^n) / 78.

(End)