Fill in the numbers according to the law: 1, 1, 2, 3, 5, 8, 13, 21, ... what should be the 10th number.
按规律填数：1、1、2、3、5、8、13、21、…第10个数应该是多少．
<gadget id="calculator">13 + 21</gadget>
<output>34</output>

<gadget id="calculator">34 + 21</gadget>
<output>55</output>

<result>55</result>