Pleasant Goat opens a book and finds that the product of the page numbers of the left and right pages is 420, what is the sum of the page numbers of these two pages?
喜羊羊打开一本书，发现左右两页的页码数的乘积是420，则这两页的页码数的和是多少．
<gadget id="calculator">20 + 21</gadget>
<output>41</output>

<result>41</result>