A191480 - OEIS

%I #8 Apr 11 2022 12:44:08

%S 2,8,51,624,14937,660986,54708660,8491650283,2464559025659,

%T 1339399598735349,1362655720519108653,2594569727636065556778,

%U 9247397059247356652311714,61693653372161864968465187134

%N Number of n X n symmetric binary matrices with each 1 adjacent to no more than 4 king-move neighboring 1's.

%H R. H. Hardin, <a href="/A191480/b191480.txt">Table of n, a(n) for n = 1..16</a>

%e Some solutions for n=4

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

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

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

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

%K nonn

%O 1,1

%A _R. H. Hardin_, Jun 03 2011