There are three signal flares, red, yellow, and green. If one shot, two shots or three shots are fired into the sky to indicate different signals (2) the order of the above shots is different to indicate different signals), how many different signals can be expressed.
有红、黄、绿三颗信号弹，若向天空发1枪、2枪或3枪表示不同的信号2发以上顺序不同表示不同信号)，则可以表示多少种不同的信号．
<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">3 * 2 * 1</gadget>
<output>6</output>

<gadget id="calculator">3 + 6 + 6</gadget>
<output>15</output>

<result>15</result>