Sixty-three is not a prime number. Sixty-three is classified as a composite number because it has divisors, and can be composed of other numbers than number one. More »

The positive number factors of the number 63 are: 1, 3, 7, 9, 21, and 63. The easiest way to find the factors of a number is through a series of equations that use basic division. More »

The number 121 is not a prime number. A prime number must have only two factors, 1 and the number itself. However, the number 121 has three factors as 11 is a also factor of 121 in addition to 1 and 121 itself. More »

The number 51 is not a prime number; it is a composite number. A prime number is any positive number that can be divided evenly only by the number 1 and itself. More »

The number 21 is not a prime number. Prime numbers are numbers greater than one that are evenly divisible by only 1 and themselves. As the number 21 has multiple factors, including 1, 21, 3 and 7, it does not meet the de... More »

The number 19 is the eighth prime number. A prime number is a positive, whole number that is only divisible by one and itself. Nineteen is also the seventh Mersenne prime exponent, which is a prime number that is one les... More »

Eighty-nine is a prime number. To check for a prime number, divide it by every number from two to one less than the number (88 in this case). If no smaller number can be evenly divided into the number, which is the case ... More » Math Numbers