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%I #5 Dec 18 2015 18:17:39
%S 1,1,3,11,47,294,2274,23217,346865,7054923,194307949,7369451741,
%T 380583130482,26850075718493,2600396553939968,344812336151621752,
%U 62585126371789861439,15557855832828751119291
%N Number of n X n symmetric binary matrices with each 1 adjacent to exactly 2 horizontally, vertically or diagonally neighboring 1s
%e Some solutions for n=4
%e ..0..1..1..0....0..0..0..0....0..0..0..0....1..1..0..0....1..1..1..0
%e ..1..1..0..1....0..0..1..1....0..1..1..0....1..0..1..0....1..0..0..1
%e ..1..0..0..1....0..1..0..1....0..1..0..1....0..1..0..1....1..0..0..1
%e ..0..1..1..1....0..1..1..0....0..0..1..1....0..0..1..1....0..1..1..1
%K nonn
%O 1,3
%A _R. H. Hardin_ May 30 2011