For all positive integers $$x$$, let $f(x)=\begin{cases}1 &\mbox{if x = 1}\\ \frac x{10} &\mbox{if x is divisible by 10}\\ x+1 &\mbox{otherwise}\end{cases}$ and define a sequence as follows: $$x_1=x$$ and $$x_{n+1}=f(x_n)$$ for all positive integers $$n$$. Let $$d(x)$$ be the smallest $$n$$ such that $$x_n=1$$. (For example, $$d(100)=3$$ and $$d(87)=7$$.) Let $$m$$ be the number of positive integers $$x$$ such that $$d(x)=20$$. Find the sum of the distinct prime factors of $$m$$.

(第二十二届AIME1 2004 第15题)