420;
4 + 2 + 0 = 6
69;
6 + 9 = 15
1 + 5 = 6
6 = 6
420 = 69
@Ophillous fun fact: digital root is just (x mod 9).
sure, if you get 0 from (x mod 9) and you didn't put 0 in, then you should actually return 9, but still it's an interesting little observation