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A228755 Number of 3 X n binary arrays with top left element equal to 1 and no two ones adjacent horizontally or antidiagonally. 1
4, 8, 39, 126, 482, 1712, 6277, 22700, 82580, 299648, 1088499, 3952186, 14352786, 52119040, 189266297, 687294648, 2495834292, 9063317432, 32912374319, 119517358582, 434013128786, 1576067091632, 5723300581661, 20783486354532 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

FORMULA

Empirical: a(n) = 2*a(n-1) + 6*a(n-2) - a(n-4).

Empirical g.f.: x*(2 - x)*(2 + x) / (1 - 2*x - 6*x^2 + x^4). - Colin Barker, Sep 12 2018

EXAMPLE

Some solutions for n=4:

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

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

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

CROSSREFS

Row 3 of A228754.

Sequence in context: A032056 A214535 A321717 * A007215 A195677 A062753

Adjacent sequences:  A228752 A228753 A228754 * A228756 A228757 A228758

KEYWORD

nonn

AUTHOR

R. H. Hardin, Sep 02 2013

STATUS

approved

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Last modified August 18 04:50 EDT 2019. Contains 326072 sequences. (Running on oeis4.)