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%I #6 Dec 18 2015 18:17:56
%S 1,19,415,31753,6221993,3573771563
%N Number of zero-sum n X n -1..1 arrays with every element unequal to at most two horizontal and vertical neighbors
%C Diagonal of A202047
%e Some solutions for n=4
%e .-1.-1..0.-1...-1..1..1.-1....0..0..0..1...-1..0..0..1...-1.-1..0.-1
%e ..1..0..0..0...-1.-1.-1.-1....1..0..0..1....0..0..0.-1....1..1..0..0
%e ..1..0..0..0....1..1..1..1....1.-1.-1..1....1..1..0.-1....1..1..1..1
%e ..0..1..1.-1....1..0..0.-1....0.-1.-1.-1....0..1..0.-1...-1.-1.-1..0
%K nonn
%O 1,2
%A _R. H. Hardin_ Dec 10 2011
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