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A055549
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Number of normal n X n (-1,0,1)-matrices.
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3
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OFFSET
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1,1
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REFERENCES
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W. H. Press et al., Numerical Recipes, Cambridge, 1986; Chapter 11.
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LINKS
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MATHEMATICA
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normalQ[a_] := Block[{b=Transpose[a]}, a.b === b.a]; cnt[n_]:= Block[{c=0, q=n^2}, Do[If[normalQ@Partition[IntegerDigits[t-1, 3, q]-1, n], c++ ], {t, 3^q}]; c]; Array[cnt, 4]; - Giovanni Resta, Apr 03 2006
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CROSSREFS
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KEYWORD
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nonn,more,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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