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 A271570 Number of distinct eigenvalues of n X n matrices with elements {-1, 0, +1}. 4
 3, 21, 375, 24823 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES Steven E. Thornton & Robert M. Corless, The Bohemian Eigenvalue Project, Poster Presented at The International Symposium on Symbolic and Algebraic Computation (ISSAC 2016). Wilfrid Laurier University, July 19-22, 2016. LINKS Table of n, a(n) for n=1..4. Robert Corless and Steven Thornton, The Bohemian Eigenvalue Project, 2017 poster. Steven E. Thornton, GitHub repository for code used to generate this sequence. Steven E. Thornton & Robert M. Corless, The Bohemian Eigenvalue Project. FORMULA a(n) <= 3^(n^2). - Robert P. P. McKone, Sep 16 2023 MATHEMATICA (* Program not suitable to compute more than 3 terms *) a[n_] := Module[{r, iter}, iter = Table[{r[k], {-1, 0, 1}}, {k, 1, n^2}]; Eigenvalues /@ (Table[Table[(r[# + j]& /@ Range[n]), {j, 0, n^2 - n, n}], Sequence @@ iter // Evaluate] // Flatten[#, n^2 - 1]&) // Flatten // Union // Length]; Table[an = a[n]; Print["a(", n, ") = ", an]; an, {n, 1, 3}] (* Jean-François Alcover, Jun 17 2018 *) CROSSREFS Number of characteristic polynomials: A272658. Cf. A060722. Sequence in context: A353321 A108716 A358950 * A084620 A120603 A336578 Adjacent sequences: A271567 A271568 A271569 * A271571 A271572 A271573 KEYWORD nonn,more,hard AUTHOR Steven E. Thornton, Jul 13 2016 STATUS approved

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Last modified December 4 21:08 EST 2023. Contains 367565 sequences. (Running on oeis4.)