Eight natural numbers are arranged in a row, starting from the third number, each number is the sum of the two numbers before it. Given that the fifth number is 7, what is the eighth number?
八个自然数排成一排，从第三个数开始，每个数都是它前面的两个数的和．已知第五个数是7，则第八个数是多少．
<gadget id="calculator">8 * 2</gadget>
<output>16</output>

<gadget id="calculator">16 + 13</gadget>
<output>29</output>

<result>29</result>