

A269635


Number of lengthn 0..3 arrays with no repeated value differing from the previous repeated value by other than plus two or minus 1.


1



4, 16, 60, 221, 796, 2828, 9928, 34537, 119236, 409098, 1396288, 4744671, 16062116, 54199810, 182382428, 612236251, 2050883956, 6857469364, 22892085300, 76311433969, 254067536796, 844941922160, 2807225267056, 9318543171653
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OFFSET

1,1


LINKS



FORMULA

Empirical: a(n) = 9*a(n1)  21*a(n2)  19*a(n3) + 93*a(n4) + 27*a(n5)  133*a(n6)  87*a(n7).
Empirical g.f.: x*(4  20*x + 93*x^3  x^4  151*x^5  89*x^6) / ((1  3*x)*(1  6*x + 3*x^2 + 28*x^3  9*x^4  54*x^5  29*x^6)).  Colin Barker, Jan 25 2019


EXAMPLE

Some solutions for n=9:
..2. .1. .2. .1. .2. .0. .2. .1. .1. .1. .1. .3. .3. .0. .0. .2
..0. .2. .3. .3. .2. .1. .0. .3. .3. .2. .3. .0. .1. .2. .2. .0
..3. .0. .0. .0. .1. .3. .0. .2. .2. .2. .0. .1. .3. .0. .1. .3
..1. .3. .2. .1. .0. .2. .1. .3. .1. .0. .3. .1. .0. .1. .3. .1
..0. .0. .2. .1. .3. .0. .0. .2. .3. .2. .1. .0. .3. .2. .0. .2
..1. .1. .0. .2. .2. .2. .2. .0. .2. .3. .2. .3. .0. .1. .3. .3
..3. .3. .3. .0. .3. .3. .2. .1. .0. .1. .0. .2. .0. .2. .2. .1
..0. .3. .2. .1. .1. .2. .1. .2. .1. .3. .2. .0. .2. .3. .0. .0
..0. .0. .0. .0. .2. .0. .3. .1. .0. .1. .2. .2. .0. .2. .3. .2


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



