A Shanghai telephone number has 7 digits, the first digit of which is not 0, and the digits are not repeated. How many such telephone numbers are there?
上海电话号码有7个数码，其中第一个数字不为0，而且数字不重复，这样的电话号码共有多少个？
<gadget id="calculator">9 * 9 * 8 * 7 * 6 * 5 * 4</gadget>
<output>544_320</output>

<result>544_320</result>