%I #9 Mar 27 2018 09:36:44
%S 1,4,7,12,26,51,97,193,380,741,1456,2860,5605,10997,21581,42332,83047,
%T 162936,319650,627099,1230289,2413641,4735192,9289761,18225136,
%U 35754992,70146009,137616081,269982313,529665276,1039124759,2038608652,3999447882
%N Number of n X 4 binary arrays with each 1 adjacent to exactly one 1 vertically and one 1 horizontally.
%C Equivalent to all 1s connected only in 2 X 2 blocks.
%C Column 4 of A183342.
%H R. H. Hardin, <a href="/A183336/b183336.txt">Table of n, a(n) for n = 1..200</a>
%F Empirical: a(n) = a(n1) + a(n2) + 2*a(n3)  a(n5).
%F Empirical g.f.: x*(1 + x)^2*(1 + x  x^2) / (1  x  x^2  2*x^3 + x^5).  _Colin Barker_, Mar 27 2018
%e Some solutions for 5 X 4:
%e ..0..0..0..0....0..0..0..0....1..1..0..0....0..0..0..0....0..1..1..0
%e ..0..0..0..0....0..0..0..0....1..1..0..0....0..1..1..0....0..1..1..0
%e ..0..0..1..1....0..0..0..0....0..0..0..0....0..1..1..0....0..0..0..0
%e ..0..0..1..1....0..0..1..1....0..1..1..0....0..0..0..0....1..1..0..0
%e ..0..0..0..0....0..0..1..1....0..1..1..0....0..0..0..0....1..1..0..0
%Y Cf. A183342.
%K nonn
%O 1,2
%A _R. H. Hardin_, Jan 04 2011
