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%I #7 Dec 18 2015 18:17:39
%S 2,5,25,195,2475,53324,1872113,109037035,10508450377,1672058437225,
%T 440124911303718,191498508664286039,137739615464486164780,
%U 163796811382099494131871,322006666961136384120723488
%N Number of n X n symmetric binary matrices with each 1 adjacent to no more than 1 horizontally or vertically neighboring 1
%H Ron Hardin, <a href="/A191506/b191506.txt">Table of n, a(n) for n = 1..26</a>
%e Some solutions for n=4
%e ..1..0..1..0....0..0..0..1....0..1..0..0....0..0..0..1....1..0..0..1
%e ..0..1..0..1....0..0..0..1....1..0..0..0....0..0..1..0....0..1..0..0
%e ..1..0..1..0....0..0..1..0....0..0..1..0....0..1..0..0....0..0..0..1
%e ..0..1..0..1....1..1..0..1....0..0..0..1....1..0..0..1....1..0..1..0
%K nonn
%O 1,1
%A _R. H. Hardin_ Jun 04 2011
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