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%I #6 Mar 30 2012 18:37:43
%S 1,4,28,334,7906
%N Number of real invertible (0,1) n X n matrices with (-1,0,1) inverses.
%e {{1,1,1,1,0},{1,1,1,0,1},{1,1,1,1,1},{1,0,1,1,0},{0,1,1,0,0}} qualifies since its inverse is
%e {{1,1,-1,0,-1},{1,0,0,-1,0},{-1,0,0,1,1},{0,-1,1,0,0},{-1,0,1,0,0}}
%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 && Union[Flatten[{Inverse[q], {-1, 0, 1}}]]==={-1, 0, 1}], {n, 5}]
%K hard,nonn
%O 1,2
%A _Wouter Meeussen_, Aug 25 2003
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