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%I #6 Dec 18 2015 18:17:40
%S 2,8,58,856,24368,1348666,145634012,30602076600,12521664597022,
%T 9976791553569412,15477885230123717308,46755695360925385415444,
%U 275015972447150661617296526,3149789884136909401259248638902
%N Number of n X n symmetric binary matrices with each 1 adjacent to no more than 4 horizontally, vertically or diagonally neighboring 1s
%H R. H. Hardin, <a href="/A191603/b191603.txt">Table of n, a(n) for n = 1..18</a>
%e Some solutions for n=4
%e ..1..0..0..1....0..0..0..0....0..1..0..1....0..1..1..0....0..1..1..1
%e ..0..1..1..1....0..0..0..1....1..0..1..1....1..0..0..1....1..1..0..1
%e ..0..1..0..1....0..0..1..0....0..1..0..0....1..0..1..0....1..0..1..0
%e ..1..1..1..0....0..1..0..1....1..1..0..0....0..1..0..1....1..1..0..1
%K nonn
%O 1,1
%A _R. H. Hardin_ Jun 08 2011
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