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 A211708 #10 Aug 11 2015 17:41:04 %S A211708 1,18,588,30240,2277600,234440280,31448589480 %N A211708 Number of n X 3 nonnegative integer arrays with new values 0 upwards introduced in row major order and every value unique in its row and column. %C A211708 Column 3 of A211709. %e A211708 Some solutions for n=4: %e A211708 ..0..1..2....0..1..2....0..1..2....0..1..2....0..1..2....0..1..2....0..1..2 %e A211708 ..2..3..0....1..3..0....1..0..3....3..0..1....1..0..3....1..0..3....1..0..3 %e A211708 ..1..2..3....2..0..1....2..3..0....1..2..0....3..2..1....2..3..4....2..3..1 %e A211708 ..3..0..1....3..4..5....3..2..1....2..3..4....2..3..0....3..5..6....3..2..0 %K A211708 nonn %O A211708 1,2 %A A211708 _R. H. Hardin_, Apr 19 2012