|
%I #4 Apr 06 2012 11:01:15
%S 64,322,1602,7994,39770,197618,980042,4851354,23971042,118229026,
%T 582129930,2861563514,14044992402,68835873986,336921033210,
%U 1647038902058,8042362627394,39229027769714,191167187783274,930758796100442
%N Number of (n+1)X(n+1) -6..6 symmetric matrices with every 2X2 subblock having sum zero and three or four 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="/A211258/b211258.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 13*a(n-1) +13*a(n-2) -721*a(n-3) +779*a(n-4) +18689*a(n-5) -25301*a(n-6) -297919*a(n-7) +287578*a(n-8) +3113878*a(n-9) -880464*a(n-10) -20368976*a(n-11) -8788232*a(n-12) +71301440*a(n-13) +72542540*a(n-14) -93705748*a(n-15) -122099536*a(n-16) +82149632*a(n-17) +97618464*a(n-18) -62699504*a(n-19) -36898656*a(n-20) +34352128*a(n-21) +226560*a(n-22) -8062208*a(n-23) +3326976*a(n-24) -568320*a(n-25) +36864*a(n-26)
%e Some solutions for n=3
%e .-6..1.-5..1...-5..4..0..2...-6..0.-3..0...-5..2..0..2....2..0.-2.-3
%e ..1..4..0..4....4.-3.-1.-1....0..6.-3..6....2..1.-3..1....0.-2..4..1
%e .-5..0.-4..0....0.-1..5.-3...-3.-3..0.-3....0.-3..5.-3...-2..4.-6..1
%e ..1..4..0..4....2.-1.-3..1....0..6.-3..6....2..1.-3..1...-3..1..1..4
%K nonn
%O 1,1
%A _R. H. Hardin_ Apr 06 2012
| 