In a pile of steel pipes, there are 2 steel pipes in the uppermost layer, 11 steel pipes in the lowest layer, and the difference between two adjacent layers is 1 steel pipe. How many steel pipes are there in the stack of 10 layers?
一堆钢管，最上层有2根，最下层有11根，相邻两层相差1根，共10层这堆钢管一共有多少根．
<gadget id="calculator">2 + 11</gadget>
<output>13</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">13 * 5</gadget>
<output>65</output>

<result>65</result>