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%I #11 Apr 05 2020 22:20:37
%S 4,16,62,240,932,3620,14056,54576,211912,822832,3194960,12405648,
%T 48169664,187037120,726243040,2819915904,10949400256,42515227456,
%U 165081604736,640992365568,2488897617536,9664095367424,37524540428032
%N Number of n X 2 0,1 arrays indicating 2 X 2 subblocks of some larger (n+1) X 3 binary array having two adjacent 1's and two adjacent 0's.
%H R. H. Hardin, <a href="/A227438/b227438.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 4*a(n-1) - 2*a(n-2) + 6*a(n-3).
%F Empirical g.f.: 2*x*(2 + 3*x^2) / (1 - 4*x + 2*x^2 - 6*x^3). - _Colin Barker_, Sep 08 2018
%e Some solutions for n=4:
%e ..1..0....1..0....1..0....0..0....1..0....1..1....1..1....0..1....0..0....1..1
%e ..0..1....1..0....1..0....0..0....1..0....0..0....0..1....1..0....1..0....0..0
%e ..1..1....1..1....1..0....1..0....1..0....1..1....0..1....0..0....0..0....1..0
%e ..0..0....0..1....0..1....0..0....1..0....0..1....1..1....0..0....1..1....0..0
%Y Column 2 of A227442.
%K nonn
%O 1,1
%A _R. H. Hardin_ Jul 11 2013
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