%I #6 Apr 26 2021 21:27:50
%S 4,51,1675,125483,20178747,6756016331,4647730539387,6537458079419739,
%T 18773661532321526331,110047493954215211056859
%N Number of (n+1) X (n+1) 0..3 symmetric matrices with every 2 X 2 subblock having one, two or four distinct values, and new values 0..3 introduced in lower triangle row major order.
%e Some solutions for n=3
%e ..0..1..2..3....0..1..2..3....0..1..1..3....0..1..0..0....0..1..1..1
%e ..1..0..3..3....1..1..1..0....1..1..1..3....1..0..0..2....1..1..1..1
%e ..2..3..0..0....2..1..2..3....1..1..2..0....0..0..1..3....1..1..1..1
%e ..3..3..0..0....3..0..3..2....3..3..0..0....0..2..3..1....1..1..1..0
%K nonn
%O 1,1
%A _R. H. Hardin_ Mar 27 2012
