pile of circular steel pipes are stacked together, and its cross-section is in the shape of an isosceles trapezoid. It is known that there are 8 steel pipes in the top layer and 13 steel pipes in the bottom layer, and the bottom layer is 1 more than the top layer. Find the total number of pipes in this pile.
一堆圆形钢管堆在一起，它的横截面形状成等腰梯形．已知这堆钢管最上面一层有8根，最下面的一层有13根，并且下面一层都比上面一层多1根．求这堆钢管共有多少根．
<gadget id="calculator">8 + 13</gadget>
<output>21</output>

<gadget id="calculator">13 - 8</gadget>
<output>5</output>

<gadget id="calculator">5 + 1</gadget>
<output>6</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">21 * 3</gadget>
<output>63</output>

<result>63</result>