Blocks of phone numbers

Mastertel offers its customers blocks of telephone numbers - a sequence of 10, 50, 100, 1000, etc. numbers in a row. In practice, such blocks are often used by call centers. Assuming that their phone number may be black-listed, they set aside blocks of telephone numbers so that they may continue to operate. The more such 'blocks of numbers' the company has, the more telephone numbers it has.

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