Since this has a factual answer, I’ll move it to GQ for you.
Cajun Man ~ SDMB Moderator
Once you add the sum of any two didgit number, and the subtract that sum from the original, it’s always a multiple of nine.
The only possible numbers are:
81
72
63
54
45
36
27
18
9
And those are always the same symbols
Your link is taking forever to load for me, but it sounds like the same thing Snopes describes here.