A pile of logs has 7 layers, the first layer has 2 logs, and each layer below has 1 log more than the upper layer. How many logs are there in total?
一堆圆木共7层，第一层有2根，下面每层比上层多1根，这堆圆木共多少根？
<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">2 + 6 + 2</gadget>
<output>10</output>

<gadget id="calculator">7 / 2</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">10 * (7/2)</gadget>
<output>35</output>

<result>35</result>