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 A272662 #15 Sep 30 2023 18:19:05
%S A272662 1,2,6,28,203,3150,131641
%N A272662 Number of distinct characteristic polynomials of n X n matrices with elements {-1, +1}.
%D A272662 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.)
%o A272662 (Python)
%o A272662 from itertools import product
%o A272662 from sympy import Matrix
%o A272662 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
%Y A272662 Six classes of matrices mentioned in Rob Corless's talk: A272658, A272659, A272660, A272661, A272662, A272663.
%K A272662 nonn,more
%O A272662 0,2
%A A272662 _N. J. A. Sloane_, May 15 2016
%E A272662 a(5) and a(6) from _Steven E. Thornton_, Mar 09 2019
%E A272662 a(0)=1 prepended by _Alois P. Heinz_, Sep 28 2023