## For all k|n => k|f(n) What can k be?

$n=\overline{a_1a_2\dots a_n}$ and define $f(n)=\overline{a_na_{n-1}\dots a_1}$. Find all the positive $k$ integers to which $k|f(n)$ if $k|n$ (in other words: for any multiple of $k$ (which is $n$) $k|f(n)$).