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 A055549 Number of normal n X n (-1,0,1)-matrices. 3
 3, 33, 939, 75041, 15901363, 10833591489 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES W. H. Press et al., Numerical Recipes, Cambridge, 1986; Chapter 11. LINKS Georg Muntingh, Sage code for recursively computing higher entries Eric Weisstein's World of Mathematics, Normal Matrix. MATHEMATICA 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 CROSSREFS Cf. A055547, A055548. Sequence in context: A234715 A126466 A002112 * A086894 A255930 A255883 Adjacent sequences:  A055546 A055547 A055548 * A055550 A055551 A055552 KEYWORD nonn,more,hard AUTHOR EXTENSIONS a(4) from Giovanni Resta, Apr 03 2006 a(5) from Georg Muntingh, Feb 03 2014 a(6) from Bert Dobbelaere, Sep 20 2020 STATUS approved

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Last modified June 23 21:09 EDT 2021. Contains 345402 sequences. (Running on oeis4.)