A269601 Number of length-n 0..2 arrays with no repeated value differing from the previous repeated value by one or less.

3, 9, 24, 62, 154, 376, 902, 2142, 5040, 11786, 27418, 63544, 146822, 338478, 778944, 1790282, 4110730, 9432424, 21633542, 49603134, 113717328, 260691722, 597649402, 1370287384, 3142264070, 7206988878, 16533117792, 37935980618, 87065571946

Offset: 1

Author

R. H. Hardin, Mar 01 2016

Keywords

• nonn

Examples

			Some solutions for n=7:
..2. .2. .2. .2. .2. .0. .1. .0. .2. .2. .2. .1. .0. .1. .2. .2
..1. .1. .1. .1. .0. .2. .2. .2. .0. .0. .1. .2. .2. .2. .0. .1
..2. .1. .0. .2. .2. .1. .1. .2. .0. .1. .0. .2. .1. .1. .1. .0
..0. .2. .2. .1. .1. .0. .1. .1. .2. .1. .1. .0. .0. .0. .0. .1
..1. .1. .0. .0. .0. .2. .2. .0. .0. .0. .0. .1. .2. .1. .1. .2
..1. .0. .1. .2. .2. .0. .0. .2. .1. .1. .0. .2. .1. .0. .0. .1
..2. .1. .0. .0. .1. .0. .1. .0. .2. .2. .2. .0. .1. .2. .1. .0
		

Links

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

Crossrefs

Column 2 of A269606.

Formula

Empirical: a(n) = 5*a(n-1) - 5*a(n-2) - 8*a(n-3) + 12*a(n-4).

Empirical g.f.: x*(3 - 6*x - 6*x^2 + 11*x^3) / ((1 - 2*x)^2*(1 - x - 3*x^2)). - Colin Barker, Jan 24 2019