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%I #4 Nov 15 2013 19:29:41
%S 4,18,64,236,888,3336,12512,46928,176032,660320,2476928,9291200,
%T 34852224,130734208,490397184,1839529216,6900259328,25883567616,
%U 97091868672,364201376768,1366156040192,5124588881920,19222848954368,72106842214400
%N Number of (n+1)X(1+1) 0..1 arrays with every element equal to some horizontal, vertical, diagonal or antidiagonal neighbor, with top left element zero
%C Column 1 of A231957
%H R. H. Hardin, <a href="/A231950/b231950.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 4*a(n-1) -2*a(n-2) +4*a(n-3)
%e Some solutions for n=7
%e ..0..0....0..0....0..0....0..0....0..0....0..0....0..0....0..0....0..1....0..1
%e ..0..0....0..0....1..0....0..1....0..0....0..1....0..1....1..0....1..0....0..1
%e ..0..1....0..0....1..0....1..0....0..0....0..1....1..1....1..1....0..1....0..0
%e ..0..1....1..0....1..0....1..0....1..0....0..0....0..1....0..1....0..1....1..0
%e ..1..1....0..1....0..0....1..0....0..1....0..0....0..1....0..1....1..0....0..1
%e ..0..1....1..0....0..1....0..1....0..1....1..1....1..0....1..1....0..0....0..1
%e ..1..0....0..1....1..1....1..0....1..0....0..1....1..0....0..0....1..0....1..0
%e ..0..1....1..1....0..0....0..0....0..0....0..1....0..1....1..1....1..0....0..0
%K nonn
%O 1,1
%A _R. H. Hardin_, Nov 15 2013
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