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%I #6 Mar 31 2012 17:11:39
%S 15,891,208575,192515373,700590250755,10052185332068649,
%T 568662258529219221297,126836971252795362522842613,
%U 111541083171262765512515480985165
%N 1/4 the number of (n+1)X(n+1) 0..3 symmetric matrices with every 2X2 subblock having two, three or four distinct values
%H R. H. Hardin, <a href="/A211109/b211109.txt">Table of n, a(n) for n = 1..15</a>
%e Some solutions for n=3
%e ..2..2..3..1....2..2..1..3....0..0..0..0....0..0..1..2....2..0..3..1
%e ..2..0..0..1....2..0..1..3....0..2..2..0....0..2..1..3....0..2..3..0
%e ..3..0..1..2....1..1..1..0....0..2..1..2....1..1..3..2....3..3..0..2
%e ..1..1..2..1....3..3..0..1....0..0..2..3....2..3..2..3....1..0..2..0
%K nonn
%O 1,1
%A _R. H. Hardin_ Mar 31 2012