Two is the only even prime number because other even numbers have at least three or more positive divisors. A number can only be considered prime when it only has two positive divisors: itself and 1.
Know MoreEven numbers that are higher than 2 are composite numbers, because they have already themselves, 2 and 1 as definite divisors. There is an infinite number of primes, all of which (except the number 2) are odd numbers. A simple way to determine the primality of a number is through trial division, which is done by dividing the number starting with the divisor 2 and up to the number's square root. If any of the quotients doesn't have a remainder, then the number is not a prime number.
Learn more about NumbersThe number 67 is a prime number by definition. A prime number is any positive number that can only be divided evenly by the number one and itself. It must also be a whole number greater than one, no fractions or decimals.
Full Answer >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 definition of a prime number.
Full Answer >The number 33 is not a prime number. Prime numbers only have factors of themselves and 1. The positive factors of 33 are 1, 3, 11 and 33.
Full Answer >Fifteen is not a prime number. A prime number is a positive number that has only two possible divisors, 1 and itself. Fifteen can be divided by 3 and 5 as well as 1 and itself.
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