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A317759
Number of nX2 0..1 arrays with every element unequal to 0, 1 or 2 horizontally, vertically or antidiagonally adjacent elements, with upper left element zero.
3
2, 6, 10, 20, 42, 89, 190, 407, 873, 1874, 4024, 8642, 18561, 39866, 85627, 183917, 395034, 848492, 1822474, 3914489, 8407926, 18059375, 38789713, 83316386, 178955184, 384377666, 825604417, 1773314930, 3808901427, 8181135701
OFFSET
1,1
COMMENTS
Column 2 of A317764.
LINKS
FORMULA
Empirical: a(n) = 2*a(n-1) +a(n-2) -a(n-3) -a(n-4) for n>6
EXAMPLE
Some solutions for n=5
..0..0. .0..1. .0..1. .0..0. .0..0. .0..0. .0..0. .0..0. .0..1. .0..0
..1..1. .1..1. .1..1. .1..1. .1..1. .0..0. .0..1. .0..1. .1..1. .0..0
..1..1. .0..0. .1..1. .1..0. .1..1. .0..0. .1..1. .1..1. .0..0. .1..1
..0..0. .0..0. .1..1. .0..0. .1..1. .0..1. .0..0. .1..1. .0..1. .1..1
..0..0. .1..1. .1..0. .0..1. .0..0. .1..1. .0..1. .1..0. .1..1. .0..0
CROSSREFS
Cf. A317764.
Sequence in context: A309846 A309874 A373006 * A014279 A050543 A025588
KEYWORD
nonn
AUTHOR
R. H. Hardin, Aug 06 2018
STATUS
approved