Pi is often written as , or the Greek letter π as a shortcut. Pi is also an irrational number, meaning it cannot be written as a fraction (formula_2), where 'a' and 'b' are integers (whole numbers). This basically means that the digits of pi that are to the right of the decimal go forever—without repeating in a pattern, and that it is impossible to write the exact value of pi as a number. Pi can only be approximated, or measured to a value that is close enough for practical purposes.