38. Find the smallest natural number divisible by 63, the sum of whose digits is 63.

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## Search for solutions
38. The smallest natural number whose sum of digits is 63 is the number written with seven nines $(9 \cdot 7=63)$. But the number 9999999 is not divisible by 7, since 9999990 is divisible by 7, and 9 is not divisible by 7. Replace 0 with the number 63. But the number 99999963 is not the smallest. To get the desired number, move 63 to the beginning of the number and you get 63999999.

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## Prime and Composite Numbers.