The manager will hand over the letters to be printed to the secretary, one at a time, and put them on the top of the envelope, and the secretary will take a letter from the top to type whenever he is free. One day a total of 9 letters were typed, and the manager handed them to the secretary in the order of the first letter, the second letter, ..., the ninth letter. At lunch, the secretary told the colleague that the eighth letter had been printed, but did not disclose other work conditions in the morning. The colleague wanted to know in what order to print. Based on the information above, how many possible sequences are there for the letters to be printed in the afternoon? (There is no letter to type is also a possibility)
经理将要打印的信件交给秘书，每次给一封，且放在信封的最上面，秘书一有空就从最上面拿一封信来打．有一天共有9封信打，经理按第1封，第2封，…，第9封的顺序交给秘书．午饭时，秘书告诉同事，已把第8封信打印好了，但未透露上午工作的其他情况，这个同事很想知道是按什么顺序来打印．根据以上信息，下午打印的信的顺序有多少种可能？(没有要打的信也是一种可能)
<gadget id="calculator">2 ** 8</gadget>
<output>256</output>

<gadget id="calculator">2 ** 7</gadget>
<output>128</output>

<gadget id="calculator">128 / 2</gadget>
<output>64</output>

<gadget id="calculator">7 * 64</gadget>
<output>448</output>

<gadget id="calculator">256 + 448</gadget>
<output>704</output>

<result>704</result>