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A207008 Number of n X 1 0..2 arrays avoiding the patterns z z+1 z or z z-1 z in any row or column. 4
3, 9, 23, 61, 161, 425, 1121, 2957, 7801, 20581, 54297, 143245, 377905, 996981, 2630217, 6938989, 18306305, 48295333, 127411801, 336135325, 886785649, 2339500565, 6172024649, 16282914765, 42957267425, 113329023173, 298982413497 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Column 1 of A207015.

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) + 2*a(n-3) + 2*a(n-4).

Empirical g.f.: x*(3 + 2*x^2 + 4*x^3) / (1 - 3*x + 2*x^2 - 2*x^3 - 2*x^4). - Colin Barker, Feb 20 2018

EXAMPLE

All solutions for n=4:

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

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

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

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

CROSSREFS

Cf. A207015.

Sequence in context: A318818 A026599 A061647 * A077996 A330453 A029852

Adjacent sequences:  A207005 A207006 A207007 * A207009 A207010 A207011

KEYWORD

nonn

AUTHOR

R. H. Hardin, Feb 14 2012

STATUS

approved

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Last modified September 21 11:17 EDT 2020. Contains 337268 sequences. (Running on oeis4.)