[Math] Telephone Numbers without repeated digits

Question

In a city with telephone numbers with $6$ digits,how many telephone numbers exist without repeated digits?What does this mean? That my telephone number shouldn't have twice the same number or that my telephone number and yours should not have the same digits?

Answer 1

It means that 122345 is not allowed, nor is 123452, because each of them includes the digit 2 twice. Only numbers like 125783 are allowed.