Divide 16 into the sum of several non-zero natural numbers, what is the maximum product of these non-zero natural numbers.
把16分成若干个非零自然数的和，这些非零自然数的乘积最大是多少．
<gadget id="calculator">3 * 3 * 3 * 3 * 2 * 2</gadget>
<output>324</output>

<result>324</result>