There are 20 squares on a large paper, put 1 grain of rice in the first square, 2 grains in the second square, 3 grains in the third square, and 4 grains in the fourth square... this big paper How many grains of rice are put on it?
一张大纸上有20个方格，第一个方格放1粒米，第二个方格放2粒，第三个方格放3粒，第四个方格放4粒…这张大纸上总共放了多少粒米．
<gadget id="calculator">1 + 20</gadget>
<output>21</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">21 * 10</gadget>
<output>210</output>

<result>210</result>