In a pile of steel pipes, every two adjacent layers have a difference of 1, the uppermost layer has 2, and the lowermost layer has 6. How many steel pipes are there in this pile?
一堆钢管，每相邻两层都相都差1根，最上层2根，最下层6根这堆钢管共多少根．
<gadget id="calculator">2 + 6</gadget>
<output>8</output>

<gadget id="calculator">6 - 2</gadget>
<output>4</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">8 * (5/2)</gadget>
<output>20</output>

<result>20</result>