When a three-digit number is divided by 21, the remainder is 17, and when divided by 20, the remainder is 17. What is the smallest number?
一个三位数除以21余17，除以20也余17．这个数最小是多少？
<gadget id="calculator">21 * 20</gadget>
<output>420</output>

<gadget id="calculator">420 + 17</gadget>
<output>437</output>

<result>437</result>