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%I #7 Apr 19 2020 23:41:45
%S 0,4,80,2876,200204,29134076,9039552112,6084192150856,
%T 8965720251221240,29122359898196696856,209490003763160695865576,
%U 3348908247850171650090422060,119286836904111393911302107179212
%N Number of n X n binary arrays with some 1 horizontally or vertically adjacent to some other 1 exactly once.
%C Diagonal of A268740.
%H R. H. Hardin, <a href="/A268734/b268734.txt">Table of n, a(n) for n = 1..26</a>
%e Some solutions for n=4
%e ..0..0..0..0. .1..0..1..0. .0..1..0..1. .0..0..1..0. .0..0..1..0
%e ..0..0..0..1. .1..0..0..1. .0..0..1..0. .1..0..1..0. .0..0..0..0
%e ..1..0..0..0. .0..1..0..0. .0..0..1..0. .0..0..0..0. .0..0..1..0
%e ..1..0..0..0. .0..0..0..0. .0..1..0..1. .0..0..0..0. .1..1..0..0
%Y Cf. A268740.
%K nonn
%O 1,2
%A _R. H. Hardin_, Feb 12 2016
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