[math-fun] A t-design that forces a magic square.

It's easy to make a square with numbers 1-16 in order. .1 .2 .3 .4 | .9 .4 .. .. .5 .6 .7 .8 | .. .. .. .. .9 10 11 12 | .. .. .. .. 13 14 15 16 | .. .. .. .. Add a second square, so that for any pair of numbers 1 to 16, the chosen pair will be in a row, column, or main diagonal in exactly one of the two squares. The first row starts 9, then 4. What is this square? Hint: it's a magic square. Ed Pegg Jr