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 A278731 #4 Nov 27 2016 07:15:14 %S A278731 456,121520,28637916,6410559865,1351385130108,268284486351027, %T A278731 50067074390669892,8732216738504713198,1415177080112634284232, %U A278731 212485358907612452321760,29562031801069787043980684 %N A278731 Number of nX5 0..3 arrays with rows in nondecreasing lexicographic order and columns in nonincreasing lexicographic order, but with exactly one mistake. %C A278731 Column 5 of A278734. %H A278731 R. H. Hardin, <a href="/A278731/b278731.txt">Table of n, a(n) for n = 1..50</a> %e A278731 Some solutions for n=2 %e A278731 ..1..3..3..2..1. .1..3..2..2..0. .3..1..2..1..0. .3..2..1..0..0 %e A278731 ..3..2..2..3..1. .2..1..1..0..2. .3..2..0..1..0. .0..1..2..1..1 %Y A278731 Cf. A278734. %K A278731 nonn %O A278731 1,1 %A A278731 _R. H. Hardin_, Nov 27 2016