Am 16.10.2011 16:50, schrieb Robert Leguillon:
Yes, correct. But when I used it unprepared a year ago I was a little bit surprised, until I started to calculate the amount of solutions, then I found it ;-)Take any two digit number, subtract the sum of the individual digits, and the result is a multiple of 9. All of the multiples of 9 correspond to the same symbol in the table, and Bob's your uncle.
