Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #5 Mar 31 2012 12:37:34
%S 4,46,1139,55516,5327304,1010944060,380704421087,285205710360936,
%T 425825333933157003,1268871858354238286927,7554384371145384136117854,
%U 89942576436863983961350601461,2143078341798100623746679385130235
%N Number of (n+1)X(n+1) 0..2 symmetric matrices with every 2X2 subblock having one or two distinct values, and new values 0..2 introduced in lower triangle row major order
%H R. H. Hardin, <a href="/A210855/b210855.txt">Table of n, a(n) for n = 1..16</a>
%e Some solutions for n=3
%e ..0..1..1..0....0..1..2..2....0..1..1..1....0..0..0..0....0..1..0..0
%e ..1..0..1..1....1..1..1..1....1..1..2..1....0..0..0..0....1..1..1..1
%e ..1..1..1..0....2..1..2..2....1..2..2..2....0..0..0..0....0..1..1..0
%e ..0..1..0..0....2..1..2..0....1..1..2..2....0..0..0..1....0..1..0..1
%K nonn
%O 1,1
%A _R. H. Hardin_ Mar 28 2012