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A213690 Half the number of (n+1)X(n+1) symmetric 0..1 arrays with no 2X2 subblock summing to 2.

%I A213690 #7 Jun 02 2025 08:03:10
%S A213690 3,13,70,529,5148,68798,1220409,29377751,949700962,41536397680,
%T A213690 2450653487731,195553849371916,21091722699002539,3077853629320011499,
%U A213690 607688763160596614184,162407853243770174812161
%N A213690 Half the number of (n+1)X(n+1) symmetric 0..1 arrays with no 2X2 subblock summing to 2.
%C A213690 Column 1 of A213697
%H A213690 R. H. Hardin, <a href="/A213690/b213690.txt">Table of n, a(n) for n = 1..18</a>
%e A213690 Some solutions for n=4
%e A213690 ..1..0..0..0..0....0..0..1..0..1....0..1..0..1..0....1..1..0..1..1
%e A213690 ..0..0..1..0..1....0..1..1..1..1....1..1..1..1..1....1..1..1..1..1
%e A213690 ..0..1..1..1..1....1..1..0..1..0....0..1..1..1..1....0..1..1..1..0
%e A213690 ..0..0..1..1..1....0..1..1..1..1....1..1..1..0..1....1..1..1..0..0
%e A213690 ..0..1..1..1..1....1..1..0..1..0....0..1..1..1..1....1..1..0..0..0
%K A213690 nonn
%O A213690 1,1
%A A213690 _R. H. Hardin_ Jun 18 2012