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1/4 the number of (n+1)X(n+1) 0..3 symmetric matrices with every 2X2 subblock having two or four distinct values
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%I #5 Mar 31 2012 17:14:19

%S 9,147,4275,226299,21796677,3826732161,1225785261321,717092242514919,

%T 766646778031785891,1498740416067587909439

%N 1/4 the number of (n+1)X(n+1) 0..3 symmetric matrices with every 2X2 subblock having two or four distinct values

%e Some solutions for n=3

%e ..2..2..2..3....1..0..1..1....1..3..2..0....2..3..2..1....0..2..0..2

%e ..2..3..2..3....0..0..0..0....3..3..2..0....3..2..2..2....2..2..2..2

%e ..2..2..3..2....1..0..1..1....2..2..2..0....2..2..3..2....0..2..3..3

%e ..3..3..2..3....1..0..1..2....0..0..0..0....1..2..2..2....2..2..3..0

%K nonn

%O 1,1

%A _R. H. Hardin_ Mar 31 2012