A phone number in USA without international dialing sequence. A phone number in USA is a

sequence of $10$ digits $(0-9).$ The digits are divided into $3$ groups: a $3-$digit area code, a $3-$digit prefix $($also

called the exchange code or central office code$),$ and a $4-$digit suffix $($also called the carrier number, line

number, or station code$).$ The area code and the prefix will never start with $0$ or $1,$ but the suffix can.

To display a phone number, we can put a pair of parentheses around the area code; leave a space

between the closing parenthesis and the prefix; and put a hyphen between the prefix and suffix. $($There

are many other commonly used formats, but we focus on this format only.$)$ For example, the main phone

number for FSU is $(910)672-1111.$