A193808 - OEIS

%I #11 Sep 06 2023 16:18:46

%S 4,23,133,1465,37741,2194501,271424321,68861945361,35194944674859,

%T 36030017205738273,73787195288621907455,302231516037239516908817,

%U 2475880105112954130388596401,40564819225226093549492737413585,1329227995803738848421582217898872529,87112285931790992384301674169215105553521

%N Number of n X n symmetric 0..3 arrays with no element equal to the difference mod 4 of any two of its horizontal and vertical neighbors.

%H R. H. Hardin, <a href="/A193808/b193808.txt">Table of n, a(n) for n = 1..20</a>

%e Some solutions for 4 X 4:

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

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

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

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

%K nonn

%O 1,1

%A _R. H. Hardin_, Aug 05 2011