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%I #10 Mar 30 2012 18:37:43
%S 1,4,32,528,18596,1280468,180452552
%N Number of real n X n invertible symmetric (0,1) matrices.
%H <a href="/index/Mat#binmat">Index entries for sequences related to binary matrices</a>
%e For n = 2 the 4 matrices are 10/01, 01/10, 11/10, 01/11.
%t triamat[li_List] := (*see A086900*); 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. A086900, A086906, A118991.
%K nonn,more
%O 1,2
%A _Wouter Meeussen_ Aug 23, 2003.
%E a(6) and a(7) from _Giovanni Resta_, May 08 2006