Inspired by Problem 2008 created by Ziko.

In mathematics, the persistence of a number is the number of times one must apply a given operation to an integer before reaching a fixed point; where further application does not change the number any more (Wikipedia).

Problem 2008 is an example of multiplicative persistence. Can you code an additive persistence ?

2718->2+7+1+8=18->1+8=9. So the persistence of 2718 is 2.

You can use the tips : num2str(666)-'0'=[6 6 6].