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 A306817 #8 Mar 12 2019 12:49:49
%S A306817 3,78,18942,41840168
%N A306817 Number of non-derogatory n X n matrices with elements {-1, 0, 1}.
%H A306817 Encyclopedia of Math, <a href="https://www.encyclopediaofmath.org/index.php/Non-derogatory_matrix">Non-derogatory matrix</a>
%H A306817 S. E. Thornton, <a href="http://www.bohemianmatrices.com/cpdb/unstructured/unstructured_n1_0_1">Properties of the Bohemian family of n x n matrices with population {-1, 0, 1}</a>, Characteristic Polynomial Database.
%Y A306817 Number of characteristic polynomials is in A272658.
%Y A306817 Number of minimal polynomials is in A271587.
%K A306817 nonn,more,hard
%O A306817 1,1
%A A306817 _Steven E. Thornton_, Mar 11 2019