Some mathematical clocks where the numbers from 1 to 12 are written in an original way.
You can print and use the clock dials. Take the challenge and make your own mathematical clock!
See also the article in Plus Magazine and some notes.
The clock with 1-2-3.
Only the digits 1,2, and 3 are used (exactly once and in this order).
With the factorial and the floor function.
With some inspiration from As easy as 1-2-3.
(Download the PDF.)