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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
OFFSET
1,2
COMMENTS
Column 4 of A183328.
LINKS
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
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jan 03 2011
STATUS
approved