12.1. Find the smallest natural number consisting of identical digits and divisible by 18.

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(5-6 \text { cl.) }
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12.1. It is clear that the desired number must be even and have a sum of digits divisible by 9. Among two-digit numbers consisting of identical digits, there is no such number. Among three-digit numbers, the number 666 fits this description. It will be the smallest.

保留源文本的换行和格式，翻译结果如下：

12.1. It is clear that the desired number must be even and have a sum of digits divisible by 9. Among two-digit numbers consisting of identical digits, there is no such number. Among three-digit numbers, the number 666 fits this description. It will be the smallest.