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%I #7 Apr 19 2020 23:41:14
%S 0,24,840,47640,5419992,1328460312,725187096504,897937832100888,
%T 2550310193527246056,16737195174968513278656,
%U 255111495114527014241534160,9064348272085612349020943764248,752834148761621410865592159869765856
%N Number of n X n 0..2 arrays with some element plus some horizontally or vertically adjacent neighbor totalling two exactly once.
%C Diagonal of A268639.
%H R. H. Hardin, <a href="/A268632/b268632.txt">Table of n, a(n) for n = 1..14</a>
%e Some solutions for n=4
%e ..0..0..0..1. .2..2..0..1. .0..0..0..0. .0..0..0..0. .1..0..1..0
%e ..1..0..0..0. .1..2..1..2. .0..1..0..0. .1..0..0..0. .2..1..2..0
%e ..0..1..0..1. .2..1..2..1. .1..0..1..0. .1..0..0..0. .1..0..1..0
%e ..0..0..0..2. .1..0..1..0. .2..0..0..0. .2..1..0..1. .0..0..0..0
%Y Cf. A268639.
%K nonn
%O 1,2
%A _R. H. Hardin_, Feb 09 2016