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A269601 Number of length-n 0..2 arrays with no repeated value differing from the previous repeated value by one or less. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

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

EXAMPLE

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

CROSSREFS

Column 2 of A269606.

Sequence in context: A117585 A317474 A279978 * A006684 A342795 A267465

Adjacent sequences:  A269598 A269599 A269600 * A269602 A269603 A269604

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 01 2016

STATUS

approved

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Last modified September 18 02:31 EDT 2021. Contains 347504 sequences. (Running on oeis4.)