A191551 - OEIS

%I #7 Dec 18 2015 18:17:39

%S 2,8,33,297,4032,91392,3461143,214272233,22066261672,3754762272000,

%T 1054824912314030,490291568481195135,376674319103188012304,

%U 478415094920126210097672,1004588343161199901448153154

%N Number of n X n symmetric binary matrices with each 1 adjacent to no more than 1 diagonally or antidiagonally neighboring 1

%H R. H. Hardin, <a href="/A191551/b191551.txt">Table of n, a(n) for n = 1..26</a>

%e Some solutions for n=4

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

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

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

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

%K nonn

%O 1,1

%A _R. H. Hardin_ Jun 05 2011