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A268735
Number of n X 3 binary arrays with some 1 horizontally or vertically adjacent to some other 1 exactly once.
1
2, 15, 80, 396, 1788, 7831, 33170, 137868, 563486, 2275119, 9091772, 36031648, 141793168, 554669335, 2158604934, 8363066408, 32273565050, 124112115647, 475807505288, 1819019281732, 6936664653476, 26392068734023, 100206016839642
OFFSET
1,1
LINKS
FORMULA
Empirical: a(n) = 4*a(n-1) + 8*a(n-2) - 24*a(n-3) - 38*a(n-4) + 4*a(n-5) + 12*a(n-6) - a(n-8).
Empirical g.f.: x*(2 + 7*x + 4*x^2 + 4*x^3 - 7*x^5 + 2*x^6) / (1 - 2*x - 6*x^2 + x^4)^2. - Colin Barker, Jan 14 2019
EXAMPLE
Some solutions for n=4:
..1..0..0. .1..0..1. .0..0..1. .1..0..0. .0..0..1. .1..0..0. .1..0..0
..1..0..0. .0..0..0. .0..0..1. .1..0..1. .0..0..1. .1..0..0. .1..0..0
..0..0..0. .1..1..0. .0..1..0. .0..0..0. .0..0..0. .0..1..0. .0..0..1
..0..0..1. .0..0..1. .0..0..0. .0..0..0. .1..0..1. .1..0..0. .1..0..0
CROSSREFS
Column 3 of A268740.
Sequence in context: A056079 A266622 A036239 * A215705 A368783 A301566
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 12 2016
STATUS
approved