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A266027
Number of n X 2 integer arrays with each element equal to the number of horizontal and antidiagonal neighbors less than itself.
1
3, 11, 55, 263, 1248, 5959, 28399, 135383, 645407, 3076736, 14667339, 69921635, 333328023, 1589030151, 7575170720, 36112097743, 172152371303, 820678962999, 3912313001599, 18650646247168, 88910730122387, 423852226145531
OFFSET
1,1
LINKS
FORMULA
Empirical: a(n) = 3*a(n-1) + 7*a(n-2) + 7*a(n-3) - a(n-4).
Empirical g.f.: x*(3 + 2*x + x^2) / (1 - 3*x - 7*x^2 - 7*x^3 + x^4). - Colin Barker, Jan 09 2019
EXAMPLE
Some solutions for n=4:
..0..2....0..0....0..1....0..0....0..0....1..0....1..0....1..0....1..0....0..0
..0..2....1..1....2..0....0..0....0..2....0..2....2..0....0..0....1..1....0..2
..1..0....0..2....0..2....0..1....0..0....1..0....1..1....0..1....0..1....1..0
..2..0....0..1....0..0....1..0....2..0....0..1....0..1....2..0....2..0....2..0
CROSSREFS
Column 2 of A266033.
Sequence in context: A095707 A259105 A242952 * A306177 A094259 A091845
KEYWORD
nonn
AUTHOR
R. H. Hardin, Dec 20 2015
STATUS
approved