Divide 21 into the sum of two natural numbers, and make the product of these two natural numbers the largest, what is the largest product.
把21分拆成两个自然数之和，且使这两个自然数的乘积最大，这个最大的乘积是多少．
<gadget id="calculator">10 * 11</gadget>
<output>110</output>

<result>110</result>