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 A249028 #9 Oct 31 2014 17:04:48 %S A249028 4,24,576,36972288,6268637952000 %N A249028 Number of 4X4X...X4 = 4^n arrays of 0's and 1's with exactly one 1 in each row, column, ..., line, ... . %e A249028 a(2)=24 because these are the 4X4 0,1 matrices representing the permutations of 4 letters. %Y A249028 Column 4 of array in A249026. %K A249028 nonn,more %O A249028 1,1 %A A249028 _N. J. A. Sloane_, Oct 23 2014