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A183325 Number of n X 4 binary arrays with each 1 adjacent to exactly two other 1s. 1
1, 4, 10, 27, 72, 179, 447, 1139, 2912, 7434, 18949, 48256, 122905, 313153, 797993, 2033404, 5181138, 13201355, 33636776, 85706587, 218381247, 556436971, 1417803304, 3612566114, 9204828661, 23453934912, 59760710321, 152270499073 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 4 of A183328.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..200

FORMULA

Empirical: a(n) = 3*a(n-1) - 2*a(n-2) + 2*a(n-3) + 2*a(n-5) - 5*a(n-7) - 3*a(n-8).

Empirical g.f.: x*(1 + x)^2*(1 - x + x^2 + 2*x^3 - 2*x^4 - 3*x^5) / (1 - 3*x + 2*x^2 - 2*x^3 - 2*x^5 + 5*x^7 + 3*x^8). - Colin Barker, Mar 27 2018

EXAMPLE

Some solutions for 8 X 4:

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

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

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

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

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

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

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

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

CROSSREFS

Cf. A183328.

Sequence in context: A122744 A192879 A077923 * A052982 A108672 A000495

Adjacent sequences:  A183322 A183323 A183324 * A183326 A183327 A183328

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jan 03 2011

STATUS

approved

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Last modified May 16 01:55 EDT 2022. Contains 353687 sequences. (Running on oeis4.)