A pile of steel pipes is piled up to form an approximate triangle. It is known that there is 1 steel pipe in the uppermost layer and 12 steel pipes in the bottom layer. The difference between two adjacent layers is 1 steel pipe.
一堆钢管，堆成一个近似三角形，已知最上层1根，最下层有12根，相邻两层之间相差1根，这堆钢管共有多少根．
<gadget id="calculator">1 + 12</gadget>
<output>13</output>

<gadget id="calculator">12 - 1</gadget>
<output>11</output>

<gadget id="calculator">11 + 1</gadget>
<output>12</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">13 * 6</gadget>
<output>78</output>

<result>78</result>