|
|
A185552
|
|
1/3 the number of n X 2 0..2 arrays with every element equal to exactly one or two of its horizontal and vertical neighbors.
|
|
1
|
|
|
1, 5, 26, 120, 576, 2768, 13256, 63544, 304608, 1460072, 6998680, 33547360, 160805064, 770799288, 3694731616, 17710240936, 84891859544, 406918677600, 1950514582792, 9349551515000, 44815924117856, 214819614744552
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
|
|
LINKS
|
|
|
FORMULA
|
Empirical: a(n) = 3*a(n-1) + 7*a(n-2) + 8*a(n-3) - 8*a(n-5).
Empirical g.f.: x*(1 - x)*(1 + 3*x + 7*x^2 + 6*x^3) / (1 - 3*x - 7*x^2 - 8*x^3 + 8*x^5). - Colin Barker, Apr 16 2018
|
|
EXAMPLE
|
Some solutions for 4 X 2 with a(1,1)=0!
..0..0....0..2....0..2....0..0....0..0....0..0....0..0....0..0....0..0....0..0
..2..2....0..2....0..2....0..0....0..1....2..1....2..2....0..1....0..2....1..1
..1..1....0..2....1..2....2..2....1..1....2..1....1..0....1..1....0..2....2..2
..2..2....1..1....1..2....2..2....2..2....0..0....1..0....0..0....0..2....0..0
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|