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A272662
Number of distinct characteristic polynomials of n X n matrices with elements {-1, +1}.
13
1, 2, 6, 28, 203, 3150, 131641
OFFSET
0,2
REFERENCES
Robert M. Corless, Bohemian Eigenvalues, Talk Presented at Computational Discovery in Mathematics (ACMES 2), University of Western Ontario, May 12 2016. (Talk based on joint work with Steven E. Thornton, Sonia Gupta, Jonathan Brino-Tarasoff, Venkat Balasubramanian.)
PROG
(Python)
from itertools import product
from sympy import Matrix
def A272662(n): return len({tuple(Matrix(n, n, p).charpoly().as_list()) for p in product((-1, 1), repeat=n**2)}) if n else 1 # Chai Wah Wu, Sep 30 2023
CROSSREFS
Six classes of matrices mentioned in Rob Corless's talk: A272658, A272659, A272660, A272661, A272662, A272663.
Sequence in context: A216187 A178446 A324126 * A125812 A093657 A355064
KEYWORD
nonn,more
AUTHOR
N. J. A. Sloane, May 15 2016
EXTENSIONS
a(5) and a(6) from Steven E. Thornton, Mar 09 2019
a(0)=1 prepended by Alois P. Heinz, Sep 28 2023
STATUS
approved