152. Find the smallest natural number that is written with identical digits and is divisible by 18.
$\triangle$ Let the desired number be denoted as

$$
\overline{a a a \ldots a} \text { ( } n \text { digits). }
$$

Since it is divisible by 18, and therefore by 2, $a$ must be an even digit.

Applying the divisibility rule for 9:

$$
(a+a+a+\ldots+a): 9, \quad \text { na:9 }
$$

Since $a$ is an even digit, the number is even.

1) Let $a=18$.

From this, the minimum possible value of $n$ is 3, from which $a=6$.

2) Now let $na$ be 36, or 54, or 72, etc.

If we take $n=3$ here, then $a$ is respectively 12, 18, 24, etc., which is impossible. Taking values of $n$ greater than 3 makes no sense.

Therefore, the desired number is the one obtained in the first case. Answer: 666.