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 A181200 #7 Dec 18 2015 18:17:26 %S A181200 0,4,756,1729728,140229804000,752239365180732000, %T A181200 419014989521191873479589920,34623595988556658225393154134784716800, %U A181200 571228532851873223553288547443139274046846826752000 %N A181200 a(n) = 0!*1!*2!*...*(n-1)! *(n^2)! *(n*(n-1))^2 / 2*n!*(n+1)!*...*(2*n-1)! %C A181200 (Empirical) Number of n X n matrices containing a defective permutation of 1..n*n in strictly increasing order rowwise and columnwise, with one permutation value omitted and one repeated (see example) %C A181200 Diagonal of A181204 %H A181200 R. H. Hardin, <a href="/A181200/b181200.txt">Table of n, a(n) for n=1..22</a> %e A181200 Some solutions for 3X3 %e A181200 ..2..3..5....1..2..5....1..2..6....1..3..4....1..3..4....1..2..4....1..3..5 %e A181200 ..4..6..7....3..4..6....3..4..8....2..5..8....2..6..7....2..5..7....2..4..6 %e A181200 ..5..8..9....4..7..9....6..7..9....4..6..9....5..7..9....3..6..9....6..7..8 %K A181200 nonn %O A181200 1,2 %A A181200 _R. H. Hardin_ Oct 10 2010