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%I #7 Jan 09 2019 09:23:35
%S 3,11,55,263,1248,5959,28399,135383,645407,3076736,14667339,69921635,
%T 333328023,1589030151,7575170720,36112097743,172152371303,
%U 820678962999,3912313001599,18650646247168,88910730122387,423852226145531
%N Number of n X 2 integer arrays with each element equal to the number of horizontal and antidiagonal neighbors less than itself.
%H R. H. Hardin, <a href="/A266027/b266027.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 3*a(n-1) + 7*a(n-2) + 7*a(n-3) - a(n-4).
%F 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
%e Some solutions for n=4:
%e ..0..2....0..0....0..1....0..0....0..0....1..0....1..0....1..0....1..0....0..0
%e ..0..2....1..1....2..0....0..0....0..2....0..2....2..0....0..0....1..1....0..2
%e ..1..0....0..2....0..2....0..1....0..0....1..0....1..1....0..1....0..1....1..0
%e ..2..0....0..1....0..0....1..0....2..0....0..1....0..1....2..0....2..0....2..0
%Y Column 2 of A266033.
%K nonn
%O 1,1
%A _R. H. Hardin_, Dec 20 2015