From the ten natural numbers from 1 to 10, choose two numbers arbitrarily and write them as ratios so that their ratios are prime numbers.
从1至10这十个自然中，任意选择两个数写成比，使它们比值是质数的共有多少个．
<gadget id="calculator">5 + 3 + 2 + 1</gadget>
<output>11</output>

<result>11</result>