Use the five numbers 2, 3, 5, 7, and 9 to perform four mixed operations. Each number can only be used once. What is the largest prime number that can be obtained?
用2、3、5、7、9这五个数字进行四则混合运算，每个数字只能用一次，能够得到的最大的质数是多少．
<gadget id="calculator">3 * 9</gadget>
<output>27</output>

<gadget id="calculator">5 * 7</gadget>
<output>35</output>

<gadget id="calculator">27 + 35</gadget>
<output>62</output>

<gadget id="calculator">62 / 2</gadget>
<output>31</output>

<result>31</result>