A268938 Number of length-n 0..2 arrays with no repeated value unequal to the previous repeated value plus one mod 2+1.

3, 9, 24, 63, 159, 396, 969, 2349, 5640, 13455, 31911, 75348, 177225, 415557, 971808, 2267631, 5281359, 12280860, 28518153, 66147165, 153274488, 354861711, 820976631, 1898144676, 4386240393, 10131006069, 23390390544, 53984735343

Offset: 1

Author

R. H. Hardin, Feb 16 2016

Keywords

• nonn

Comments

Column 2 of A268944.

Examples

			Some solutions for n=9:
..0. .1. .2. .2. .2. .1. .2. .2. .0. .2. .1. .0. .0. .0. .0. .1
..0. .2. .0. .1. .1. .0. .0. .0. .1. .1. .2. .2. .2. .2. .2. .0
..2. .0. .2. .2. .2. .1. .1. .1. .0. .0. .1. .1. .0. .0. .0. .0
..1. .2. .2. .0. .0. .0. .2. .1. .1. .0. .0. .2. .1. .0. .2. .2
..0. .0. .0. .2. .0. .1. .0. .2. .0. .1. .0. .1. .0. .2. .0. .1
..1. .2. .2. .2. .2. .1. .2. .1. .1. .1. .2. .0. .0. .0. .0. .1
..0. .1. .0. .0. .0. .0. .1. .0. .2. .0. .0. .1. .1. .1. .2. .2
..1. .0. .0. .2. .2. .2. .1. .2. .1. .2. .1. .2. .1. .1. .1. .2
..2. .2. .2. .1. .1. .0. .0. .2. .2. .1. .0. .1. .0. .2. .2. .1
		

Links

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

Crossrefs

Cf. A268944.

Formula

Empirical: a(n) = 3*a(n-1) + a(n-2) - 6*a(n-3).

Empirical g.f.: 3*x*(1 - 2*x^2) / ((1 - 2*x)*(1 - x - 3*x^2)). - Colin Barker, Mar 21 2018