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A080636
Number of real invertible (0,1) n X n matrices with (-1,0,1) inverses.
0
1, 4, 28, 334, 7906
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OFFSET
1,2
LINKS
Table of n, a(n) for n=1..5.
EXAMPLE
{{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
{{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}}
MATHEMATICA
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}]
CROSSREFS
Sequence in context:
A198513
A113371
A280570
*
A223887
A140425
A193198
Adjacent sequences:
A080633
A080634
A080635
*
A080637
A080638
A080639
KEYWORD
hard
,
nonn
AUTHOR
Wouter Meeussen
, Aug 25 2003
STATUS
approved
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Last modified April 24 04:14 EDT 2024. Contains 371918 sequences. (Running on oeis4.)