The numerator of a fraction is the product of two numbers that are reciprocals of each other, and the denominator is the sum of all prime numbers within 20. What is the fraction?
一个分数的分子是互为倒数的两个数的积，分母是20以内所有质数的和，这个分数是多少．
<gadget id="calculator">2 + 3 + 5 + 7 + 11 + 13 + 17 + 19</gadget>
<output>77</output>

<gadget id="calculator">1 / 77</gadget>
<output>1/77 = around 0.012987</output>

<result>1/77 = around 0.012987</result>