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%I #8 Nov 28 2018 11:50:56
%S 10,28,78,220,618,1740,4894,13772,38746,109020,306734,863036,2428234,
%T 6832108,19222846,54085548,152175418,428161788,1204678734,3389491996,
%U 9536696618,26832511756,75496129374,212416400780,597656166170
%N Number of (n+1) X (1+1) 0..1 arrays with every 2 X 2 subblock having one or two 1s.
%H R. H. Hardin, <a href="/A251319/b251319.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 2*a(n-1) + 3*a(n-2) - 2*a(n-3).
%F Empirical g.f.: 2*x*(5 + 4*x - 4*x^2) / (1 - 2*x - 3*x^2 + 2*x^3). - _Colin Barker_, Nov 28 2018
%e Some solutions for n=4:
%e ..1..0....1..0....0..1....1..0....1..0....0..0....0..1....0..1....0..1....0..0
%e ..0..0....1..0....0..0....1..0....1..0....1..0....0..1....0..0....1..0....1..0
%e ..1..1....1..0....1..0....1..0....0..0....0..1....0..0....1..0....0..0....0..1
%e ..0..0....0..0....1..0....1..0....1..0....0..0....0..1....0..0....0..1....0..0
%e ..1..1....1..1....1..0....1..0....1..0....0..1....0..0....1..0....0..1....1..0
%Y Column 1 of A251326.
%K nonn
%O 1,1
%A _R. H. Hardin_, Dec 01 2014