In a pile of steel pipes, there is a difference of 1 between every two adjacent layers, the uppermost layer is 2, and the lowest layer is 15. How many steel pipes are there in total?
一堆钢管，每相邻两层都相差1根，最上层2根，最下层15根，这堆钢管共多少根．
<gadget id="calculator">2 + 15</gadget>
<output>17</output>

<gadget id="calculator">15 - 2</gadget>
<output>13</output>

<gadget id="calculator">13 + 1</gadget>
<output>14</output>

<gadget id="calculator">14 / 2</gadget>
<output>7</output>

<gadget id="calculator">17 * 7</gadget>
<output>119</output>

<result>119</result>