In an article regarding symmetry, my uncle proposed a puzzle: how could you make a calendar out of seven cubes, representing the date in the format: ddmmmyy. It involves using rotational symmetries to fit all the required letters and numbers onto the cubes to be able to show every day, month and year (with a limit on the year, as it turns out.)

He went into a lot of detail about each section, covering a huge amount of languages for which it is possible, and also looked into Arabic numerals for the day and year cubes. Take a look on his blog: Maths Evangelist, for the full article.

For the day, you need the numbers 0, 1, 2, 3, 4, and 5 on the first cube, and the numbers 0, 1, 2, 6, 7, and 8 on the second cube.

For the month, you need the letters d, f, g, j, m, and o on the first cube (d can be used for p), e, l, n, r, t, and y on the second cube (n can be used for u), and a, b, c, s, u, and v on the third cube.

For the year, you need the numbers 0, 1, 2, 3, 4, and 5 on the first cube, and the numbers 1, 2, 3, 6, 7, and 8 on the second cube.