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A221536 Number of 0..2 arrays of length n with each element differing from at least one neighbor by something other than 1, starting with 0. 1
0, 2, 4, 10, 22, 54, 134, 334, 822, 2014, 4934, 12110, 29750, 73086, 179494, 440750, 1082262, 2657630, 6526342, 16026766, 39356662, 96646974, 237332966, 582812014, 1431196758, 3514554142, 8630600774, 21193942094, 52045411766, 127806567678 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 2 of A221542.

LINKS

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

FORMULA

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

Empirical g.f.: 2*x^2*(1 - x + x^2) / (1 - 3*x + 2*x^2 - 4*x^4). - 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....2....0....0....2....0....0....0....2....0....2....0

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

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

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

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

CROSSREFS

Sequence in context: A164990 A348009 A121285 * A290277 A030234 A205490

Adjacent sequences:  A221533 A221534 A221535 * A221537 A221538 A221539

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 19 2013

STATUS

approved

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Last modified August 11 07:36 EDT 2022. Contains 356055 sequences. (Running on oeis4.)