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Number of n X n symmetric binary matrices with each 1 adjacent to no more than 1 E or S neighboring 1
1

%I #6 Dec 18 2015 18:17:40

%S 2,6,34,354,6640,226090,13978062,1567580958,318961138670,

%T 117759554854782,78883071103925368,95874600035087067128,

%U 211425486715722284229326,845949075122781758953188444,6141355289964517541296446302562

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

%H R. H. Hardin, <a href="/A191742/b191742.txt">Table of n, a(n) for n = 1..36</a>

%e Some solutions for n=5

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

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

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

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

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

%K nonn

%O 1,1

%A _R. H. Hardin_ Jun 13 2011