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 A309984 #13 Aug 29 2019 20:16:11 %S A309984 0,0,0,16,0,2088,5752,199600889 %N A309984 Number of n X n Latin squares with determinant 0, divided by 2. %H A309984 Brendan McKay, <a href="https://users.cecs.anu.edu.au/~bdm/data/latin.html">Latin squares</a>. %H A309984 Hugo Pfoertner, <a href="http://www.randomwalk.de/sequences/a309258.zip">Occurrence counts of determinant values of Latin squares for n=1..8</a>, zipped (2019). %e A309984 a(4)=16: There are 2*a(4) = 32 4 X 4 Latin squares with determinant = 0, one of which is %e A309984 [1 4 3 2] %e A309984 [4 1 2 3] %e A309984 [3 2 1 4] %e A309984 [2 3 4 1]. %e A309984 An example of a 6 X 6 Latin square with determinant = 0 is %e A309984 [1 3 4 6 5 2] %e A309984 [3 2 6 5 4 1] %e A309984 [4 6 3 2 1 5] %e A309984 [6 5 1 3 2 4] %e A309984 [5 4 2 1 3 6] %e A309984 [2 1 5 4 6 3]. %Y A309984 Cf. A040082, A136609, A221976, A301371, A308853, A309258, A309985. %K A309984 nonn,more,hard %O A309984 1,4 %A A309984 _Hugo Pfoertner_, Aug 26 2019