The steel pipe factory stacks a batch of steel pipes into a pile. There are 20 steel pipes in the bottom layer, and each layer is one less than the lower layer. There are 20 layers in total. How many steel pipes are there in this batch?
钢管厂把一批钢管堆成一堆，最下面一层有20根，往上每层都比下层少1根，一共堆了20层，这批钢管共有多少根？
<gadget id="calculator">20 - 20</gadget>
<output>0</output>

<gadget id="calculator">0 + 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>