This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A272659 #23 Sep 30 2023 18:29:24
%S A272659 1,3,22,513,58335,40422490
%N A272659 Number of distinct characteristic polynomials of n X n matrices with elements {0, 1, 2}.
%H A272659 Robert M. Corless, <a href="https://www.youtube.com/watch?v=qB1KZWU8g2U">Bohemian Eigenvalues</a>, 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.)
%o A272659 (Python)
%o A272659 from itertools import product
%o A272659 from sympy import Matrix
%o A272659 def A272659(n): return len({tuple(Matrix(n,n,p).charpoly().as_list()) for p in product(range(3),repeat=n**2)}) if n else 1 # _Chai Wah Wu_, Sep 30 2023
%Y A272659 Six classes of matrices mentioned in Rob Corless's talk: A272658, A272659, A272660, A272661, A272662, A272663.
%K A272659 nonn,more
%O A272659 0,2
%A A272659 _N. J. A. Sloane_, May 15 2016
%E A272659 a(4) from _Chai Wah Wu_, Dec 03 2018
%E A272659 a(5) from _Steven E. Thornton_, Mar 09 2019
%E A272659 a(0)=1 prepended by _Alois P. Heinz_, Sep 28 2023