

A221510


Number of 0..3 arrays of length n with each element differing from at least one neighbor by 2 or more, starting with 0.


1



0, 2, 3, 12, 30, 89, 248, 706, 1995, 5652, 15998, 45297, 128240, 363074, 1027923, 2910236, 8239390, 23327177, 66043368, 186980482, 529374875, 1498754084, 4243238398, 12013359841, 34011950560, 96293859202, 272624979363
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OFFSET

1,2


COMMENTS



LINKS



FORMULA

Empirical: a(n) = a(n1) +4*a(n2) +3*a(n3) +a(n4).
Empirical g.f.: x^2*(2 + x + x^2) / ((1 + x)*(1  2*x  2*x^2  x^3)).  Colin Barker, Oct 18 2017


EXAMPLE

Some solutions for n=6
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..2....2....2....2....2....3....2....2....3....3....2....3....3....2....3....3
..3....0....2....1....2....0....0....3....1....3....3....2....0....1....2....3
..0....2....0....3....0....3....1....1....0....1....1....0....3....3....0....1
..3....2....2....0....3....0....3....1....3....3....0....3....3....3....0....0
..0....0....0....3....1....2....1....3....0....0....2....0....1....1....2....3


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



