Among the natural numbers from 1 to 20, the smallest composite number is the largest prime number.
在1-20的自然数中，最小的合数是最大质数的多少．
<gadget id="calculator">4 / 19</gadget>
<output>4/19 = around 0.210526</output>

<result>4/19 = around 0.210526</result>