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%I #8 Oct 02 2021 16:08:16
%S 1,3,39,2107,277902,87883641,66460660741,120226326939778,
%T 520179215730042235,5383068220104980704743,133236771262960489496028245
%N Number of n X n 0..3 symmetric matrices with every element equal to zero or two horizontal and vertical neighbors, and new values 0..3 introduced in lower triangle row major order.
%e Some solutions for n=4
%e ..0..1..0..3....0..0..1..1....0..1..1..1....0..1..0..1....0..1..2..3
%e ..1..2..1..2....0..0..1..1....1..1..0..1....1..0..1..2....1..0..3..1
%e ..0..1..2..3....1..1..2..0....1..0..1..1....0..1..2..0....2..3..0..0
%e ..3..2..3..1....1..1..0..1....1..1..1..2....1..2..0..2....3..1..0..0
%K nonn
%O 1,2
%A _R. H. Hardin_, Mar 29 2012
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