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Number of n X n symmetric 0..3 arrays with no element equal to any horizontal or vertical neighbor, containing at least one 3 and with new values 0..3 introduced in lower triangular row major order
1

%I #6 Dec 18 2015 18:17:42

%S 0,0,20,1436,175145,47175440,29471424170,42983780102348,

%T 146444614636063181,1165528963228211645900,21669813287663490052945610,

%U 941174635410184709958677112920,95492317441878724418372856301818197

%N Number of n X n symmetric 0..3 arrays with no element equal to any horizontal or vertical neighbor, containing at least one 3 and with new values 0..3 introduced in lower triangular row major order

%H R. H. Hardin, <a href="/A193309/b193309.txt">Table of n, a(n) for n = 1..15</a>

%e Some solutions for 4X4

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

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

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

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

%K nonn

%O 1,3

%A _R. H. Hardin_ Jul 22 2011