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 A306840 #14 May 30 2024 03:05:51
%S A306840 1,31,6891,12202161,175419087483,20540753180392401
%N A306840 Number of singular n X n matrices with elements {0, 1, 2}.
%H A306840 S. E. Thornton, <a href="http://www.bohemianmatrices.com/cpdb/unstructured/unstructured_0_1_2">Properties of the Bohemian family of n x n matrices with population {0, 1, 2}</a>, Characteristic Polynomial Database.
%H A306840 Minfeng Wang, <a href="/A306840/a306840.cpp.txt">C++ program to calculate A306840</a>
%Y A306840 Number of non-singular matrices is in A197487.
%K A306840 nonn,more,hard
%O A306840 1,2
%A A306840 _Steven E. Thornton_, Mar 12 2019
%E A306840 a(6) from _Minfeng Wang_, May 29 2024