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 A306818 #9 Mar 13 2019 03:33:04
%S A306818 3,78,19068,42300060
%N A306818 Number of non-derogatory n X n matrices with elements {0, 1, 2}.
%H A306818 Encyclopedia of Math, <a href="https://www.encyclopediaofmath.org/index.php/Non-derogatory_matrix">Non-derogatory matrix</a>
%H A306818 S. E. Thornton, <a href="http://www.bohemianmatrices.com/cpdb/unstructured/nstructured_0_1_2">Properties of the Bohemian family of n x n matrices with population {0, 1, 2}</a>, Characteristic Polynomial Database.
%Y A306818 Number of characteristic polynomials is in A272659.
%Y A306818 Number of minimal polynomials is in A306783.
%K A306818 nonn,more,hard
%O A306818 1,1
%A A306818 _Steven E. Thornton_, Mar 11 2019