a tad off topic, but is there a 'name' for, well, the following...

all numbers which add up to 3 or 9 are divisble by 3 or 9 ...
ex: 21 (2 + 1 = 3) 21 % 3 = 0
ex: 18 (1 + 8 = 9) 18 % 9 = 0
...