%I #6 Dec 18 2015 18:18:06

%S 1,5,108,7722,1640736,1033777404,1931855614272,10707730229352132,

%T 176032647122454516348,8583448868806218541129800,

%U 1241375815868250678950006865216,532497522393110319522129344363284548

%N Number of n X n 0..2 symmetric matrices with every element equal to zero, one, two or three horizontal and vertical neighbors, and new values 0..2 introduced in lower triangle row major order

%H R. H. Hardin, <a href="/A210904/b210904.txt">Table of n, a(n) for n = 1..16</a>

%e Some solutions for n=4

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

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

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

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

%K nonn

%O 1,2

%A _R. H. Hardin_ Mar 29 2012