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A221677 Number of 0..2 arrays of length n with each element differing from at least one neighbor by 1 or less, starting with 0. 1
0, 2, 5, 14, 40, 113, 320, 906, 2565, 7262, 20560, 58209, 164800, 466578, 1320965, 3739886, 10588280, 29977297, 84871040, 240284954, 680289285, 1926019518, 5452902560, 15438133441, 43708091520, 123745352482, 350345021445 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 2 of A221683.

LINKS

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

FORMULA

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

Empirical g.f.: x^2*(2 + x) / (1 - 2*x - 2*x^2 - x^3). - Colin Barker, Oct 19 2017

EXAMPLE

Some solutions for n=6

..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0

..1....1....1....1....1....1....1....0....1....0....1....1....1....0....0....1

..2....1....0....0....1....0....2....2....2....1....2....1....2....2....1....0

..0....1....0....0....1....0....2....2....0....1....0....2....1....2....0....0

..1....0....2....0....2....1....2....0....0....0....0....1....2....1....1....1

..0....1....2....1....2....1....1....0....1....1....0....2....1....0....0....0

CROSSREFS

Sequence in context: A296516 A111109 A081908 * A229737 A059505 A159035

Adjacent sequences: A221674 A221675 A221676 * A221678 A221679 A221680

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 22 2013

STATUS

approved

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Last modified February 4 17:27 EST 2023. Contains 360059 sequences. (Running on oeis4.)