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A268989
Number of n X 2 binary arrays with some element plus some horizontally or antidiagonally adjacent neighbor totalling two not more than once.
1
4, 13, 41, 126, 379, 1121, 3272, 9449, 27049, 76866, 217079, 609793, 1705036, 4748101, 13174889, 36440646, 100503667, 276476129, 758785424, 2078056481, 5680052329, 15497929098, 42216552431, 114824352001, 311871557524
OFFSET
1,1
LINKS
FORMULA
Empirical: a(n) = 6*a(n-1) - 11*a(n-2) + 6*a(n-3) - a(n-4).
Empirical g.f.: x*(4 - 11*x + 7*x^2 - x^3) / (1 - 3*x + x^2)^2. - Colin Barker, Jan 17 2019
EXAMPLE
Some solutions for n=4:
..1..0. .1..1. .1..0. .0..0. .1..0. .1..1. .0..0. .1..0. .0..0. .1..1
..0..1. .0..0. .0..1. .1..0. .1..0. .0..0. .0..0. .0..0. .1..0. .0..1
..0..1. .1..0. .0..0. .1..0. .0..0. .1..0. .0..1. .1..0. .0..0. .0..0
..1..0. .1..0. .1..0. .0..1. .0..1. .0..0. .1..0. .0..1. .1..1. .1..0
CROSSREFS
Column 2 of A268995.
Sequence in context: A070428 A320563 A368344 * A190214 A052529 A049222
KEYWORD
nonn
AUTHOR
R. H. Hardin, Feb 17 2016
STATUS
approved