The numerator of the sum of the reciprocals of two prime numbers is 31, what is the denominator of the sum.
两个质数的倒数相加和的分子是31，和的分母是多少．
<gadget id="calculator">31 - 2</gadget>
<output>29</output>

<gadget id="calculator">2 * 29</gadget>
<output>58</output>

<result>58</result>