There is a sequence: 1, 2, 4, 7, 11, 16... What is the 8th number in this sequence.
有一数列：1、2、4、7、11、16…这列数列第8个数是多少．
<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">16 + 6</gadget>
<output>22</output>

<gadget id="calculator">8 - 1</gadget>
<output>7</output>

<gadget id="calculator">22 + 7</gadget>
<output>29</output>

<result>29</result>