A train goes back and forth between Chengdu and Chongqing and stops at 7 stations. How many different hard seat tickets do you need to prepare?
一辆列车往返于成都和重庆之间，全程停靠7个车站，共需准备多少种不同的硬座车票．
<gadget id="calculator">6 + 5 + 4 + 3 + 2 + 1</gadget>
<output>21</output>

<gadget id="calculator">2 * 21</gadget>
<output>42</output>

<result>42</result>