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 A181203 #5 Jun 02 2025 03:13:09 %S A181203 0,840,360360,199536480,140229804000,118949931243000, %T A181203 117015012361447200,129624266420759510400,158211402715245473193600, %U A181203 209298196564031904834960000,296336346592302886974184080000 %N A181203 a(n)=0!*1!*2!*3!*4!*(5*n)!*10*n*(n-1) / ((n)!*(n+1)!*(n+2)!*(n+3)!*(n+4)!). %C A181203 (Empirical) Number of nX5 matrices containing a defective permutation of 1..5*n in strictly increasing order rowwise and columnwise, with one permutation value omitted and one repeated (see example) %C A181203 Column 5 of A181204 %H A181203 R. H. Hardin, <a href="/A181203/b181203.txt">Table of n, a(n) for n=1..50</a> %e A181203 Some solutions for 2X5 %e A181203 ..1..4..5..6..8....1..2..4..7..9....1..3..5..8..9....1..2..5..6..8 %e A181203 ..3..5..7..9.10....5..6..8..9.10....4..6..7..9.10....3..4..8..9.10 %K A181203 nonn %O A181203 1,2 %A A181203 _R. H. Hardin_ Oct 10 2010