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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 3 of A221515.

LINKS

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

FORMULA

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

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

Sequence in context: A025560 A247651 A305746 * A109489 A169636 A105401

Adjacent sequences:  A221507 A221508 A221509 * A221511 A221512 A221513

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 18 2013

STATUS

approved

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Last modified August 14 15:34 EDT 2022. Contains 356122 sequences. (Running on oeis4.)