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 A136609 #7 Mar 26 2018 20:34:56
%S A136609 0,0,76,14392910
%N A136609 (1/(n!)^2) * number of ways to arrange the consecutive numbers 1...n^2 in an n X n matrix with determinant = 0.
%C A136609 The computation of a(5) seems to be currently (Jan 2008) out of reach (compare with A088021(5)).
%e A136609 a(1)=0 because det((1))/=0, a(2)=0, because the only possible determinants of a matrix with elements {1,2,3,4} are +-2, +-5 and +-10.
%Y A136609 Cf. A001044, A046747, a(3)=A088215(0), a(4)=A136608(0), A221976.
%K A136609 hard,more,nonn
%O A136609 1,3
%A A136609 _Hugo Pfoertner_, Jan 21 2008