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%I #4 Apr 12 2012 06:34:06
%S 121,277,565,1101,2135,4047,7739,14661,28031,53463,102733,197579,
%T 382143,740723,1441747,2813157,5505551,10799509,21229339,41813647,
%U 82481877,162964213,322323737,638333051,1265124641,2509927951,4982252633
%N Number of (n+1)X(n+1) -8..8 symmetric matrices with every 2X2 subblock having sum zero and one or three distinct values
%C Symmetry and 2X2 block sums zero implies that the diagonal x(i,i) are equal modulo 2 and x(i,j)=(x(i,i)+x(j,j))/2*(-1)^(i-j)
%H R. H. Hardin, <a href="/A211468/b211468.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 3*a(n-1) +13*a(n-2) -43*a(n-3) -68*a(n-4) +255*a(n-5) +185*a(n-6) -810*a(n-7) -289*a(n-8) +1487*a(n-9) +292*a(n-10) -1577*a(n-11) -242*a(n-12) +895*a(n-13) +170*a(n-14) -210*a(n-15) -60*a(n-16)
%e Some solutions for n=3
%e .-1..3.-1..3...-8..0.-4..8...-4.-2.-2.-2...-3..5.-3..5....8.-6..1.-6
%e ..3.-5..3.-5....0..8.-4..0...-2..8.-4..8....5.-7..5.-7...-6..4..1..4
%e .-1..3.-1..3...-4.-4..0..4...-2.-4..0.-4...-3..5.-3..5....1..1.-6..1
%e ..3.-5..3.-5....8..0..4.-8...-2..8.-4..8....5.-7..5.-7...-6..4..1..4
%K nonn
%O 1,1
%A _R. H. Hardin_ Apr 12 2012
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