Actually this generalizes for all number of digits (down to 1) and to all multiples of 3, 9 or any number only divisible by 3. And it's not just an if, it's an

Actually this generalizes for all number of digits (down to 1) and to all multiples of 3, 9 or any number only divisible by 3. And it's not just an if, it's an iff. 132144 => 1+3+2+1+4+4 = 15 => 1+5 = 6 (divisible by 6 - obviously you can stop at 15 too)