第547题：a common divisor
What is the greatest common divisor of 45 and 63 ?
A Factor of a number is one of the two or more numbers which, multiplied together, will produce it. The multiplicand and multiplier are factors of their product.
The Divisor of a number if any number that will exactly divide it. Every divisor of a number is a factor, and every factor is a divisor. The terms factor and divisor differ only in their origin, the former implying multiplication and the latter division.
A divisor of a number is also called its measure.
A divisor of two or more numbers is called a common divisor.