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%I #10 Mar 30 2012 18:37:43
%S 1,1,5,338,14186,526876,52658844
%N Number of real n X n symmetric (0,1) matrices with positive determinant.
%H <a href="/index/Mat#binmat">Index entries for sequences related to binary matrices</a>
%e For n = 2 the only example is the identity matrix.
%t triamat[li_List] := Block[{len=Sqrt[8Length[li]+1]/2-1/2}, If[IntegerQ[len], Part[li, # ]& /@ Table[If[j>i, j(j-1)/2+i, i(i-1)/2+j], {i, len}, {j, len}], li]]; Table[it=triamat/@ IntegerDigits[Range[0, -1+2^(n(n+1)/2)], 2, n(n+1)/2]; Count[it, (q_)?MatrixQ/;(Det[q]>0)], {n, 5}]
%Y Cf. A086899, A118996.
%K nonn,more
%O 1,3
%A _Wouter Meeussen_ Aug 23, 2003.
%E a(6) and a(7) from _Giovanni Resta_, May 08 2006
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