%I #8 Feb 22 2018 12:57:30
%S 0,1,1,2,3,6,11,23,47,102,221,492,1099,2485,5637,12858,29391,67354,
%T 154539,355003,816035,1876862,4318201,9937840,22874731,52659593,
%U 121237417,279141170,642732027,1479959118,3407837387,7847200511
%N Number of n X 1 0..3 arrays with values 0..3 introduced in row major order and each element equal to one or two horizontal and vertical neighbors.
%C Column 1 of A199149.
%H R. H. Hardin, <a href="/A199142/b199142.txt">Table of n, a(n) for n = 1..200</a>
%F Empirical: a(n) = 3*a(n1) + a(n2)  7*a(n3) + a(n4) + 3*a(n5) for n>6.
%F Empirical g.f.: x^2*(1  2*x  2*x^2 + 3*x^3 + x^4) / ((1  x)*(1  x  x^2)*(1  x  3*x^2)).  _Colin Barker_, Feb 22 2018
%e Some solutions for n=8:
%e ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
%e ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
%e ..1....0....0....1....1....1....0....1....1....0....1....0....0....0....1....0
%e ..1....1....0....1....1....1....1....1....1....0....1....0....0....0....1....0
%e ..2....1....1....1....1....0....1....2....1....0....2....1....0....1....1....0
%e ..2....1....1....0....2....0....0....2....1....1....2....1....0....1....1....0
%e ..2....0....0....0....2....1....0....1....0....1....3....1....0....2....2....1
%e ..2....0....0....0....2....1....0....1....0....1....3....1....0....2....2....1
%Y Cf. A199149.
%K nonn
%O 1,4
%A _R. H. Hardin_, Nov 03 2011
