A213690 - OEIS

%I #5 Jun 18 2012 06:59:18

%S 3,13,70,529,5148,68798,1220409,29377751,949700962,41536397680,

%T 2450653487731,195553849371916,21091722699002539,3077853629320011499,

%U 607688763160596614184,162407853243770174812161

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

%C Column 1 of A213697

%H R. H. Hardin, <a href="/A213690/b213690.txt">Table of n, a(n) for n = 1..18</a>

%e Some solutions for n=4

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

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

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

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

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

%K nonn

%O 1,1

%A _R. H. Hardin_ Jun 18 2012