I was rereading one of my old A-level maths books the other day (honestly!). In the last chapter on "puzzles" they posed the following:
"Fill a 3 * 3 grid with digits 1 to 9 so that each 3 digit row number and each 3 digit column number are exactly divisible by 11."
The one I want has the total of the 3 rows and the 3 columns being maximal, and with the rows total greater than the cols total.
The end result will be
A B C
D E F
G H I
The cache may be found at N 51 9.CGG, W 0 2B.HDG