|
%I #8 May 14 2018 08:09:13
%S 1,4,14,52,190,700,2574,9476,34878,128396,472654,1739988,6405438,
%T 23580508,86807566,319567268,1176432574,4330837036,15943242574,
%U 58692346740,216065933246,795410139132,2928167715854,10779553536580
%N Number of 2n X 4 0..2 arrays with values 0..2 introduced in row major order and each element equal to exactly two horizontal and vertical neighbors.
%C Column 2 of A198285.
%H R. H. Hardin, <a href="/A198279/b198279.txt">Table of n, a(n) for n = 1..200</a>
%F Empirical: a(n) = 4*a(n-1) +a(n-2) -8*a(n-3).
%F Empirical g.f.: x*(1 - 3*x^2) / (1 - 4*x - x^2 + 8*x^3). - _Colin Barker_, May 14 2018
%e Some solutions for n=3:
%e ..0..0..1..1....0..0..1..1....0..0..0..0....0..0..1..1....0..0..1..1
%e ..0..0..1..1....0..0..1..1....0..1..1..0....0..0..1..1....0..0..1..1
%e ..1..1..2..2....2..2..2..2....0..1..1..0....2..2..0..0....2..2..2..2
%e ..1..1..2..2....2..0..0..2....0..0..0..0....2..2..0..0....2..1..1..2
%e ..0..0..1..1....2..0..0..2....2..2..1..1....0..0..2..2....2..1..1..2
%e ..0..0..1..1....2..2..2..2....2..2..1..1....0..0..2..2....2..2..2..2
%Y Cf. A198285.
%K nonn
%O 1,2
%A _R. H. Hardin_, Oct 23 2011
| 