该技术的一个限制是，对于三个小写字母加上四个数字的指定用户名格式，它仅计算600到65,000之间的编号。

A limitation of this technique is that it only calculates Numbers between 600 and 65,000 for the specified user name format of three lowercase letters followed by four digits.

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有的国家以特定的模式排列字母和数字，而另外一些国家则采用更自由的格式。

Some arrange letters and Numbers in a particular pattern; others are more free-form.

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加拿大的邮政编码格式是字母、数字、字母、一个空格、数字、字母、数字，如清单 9 所示

The Canadian postal code format, shown in Listing 9, is letter, number, letter, followed by a space, then number, letter, number

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