When a natural number is multiplied by its two adjacent even numbers, the product difference is 18. What is this natural number.
一个自然数分别与它相邻的两个偶数相乘，所得积相差18．这个自然数是多少．
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<result>9</result>