One subset is prime numbers, since their factors are only 1 and the number itself.
Other than that, there are many ways to end up with an even number of factors.
The general equation for the number of factors is (p1+1)(p2+1) ... (p3 + 1) where the p values are the exponents of the prime factors of the number. So, as long as at least one prime factor is represented oddly (i.e., there is only 1, 3, 5... so on factors of that value in the prime factorization), then the number will have an even number of factors.
All nonzero numbers have factors. Some factors are even numbers, some factors are odd numbers.
Factor rainbows display the prime factors of a given number. Some numbers, Like 27, have an odd number of prime factors. Some numbers, like 81, have an even number of prime factors.
In mathematics, all nonzero numbers have factors. Some factors are even numbers, some are odd. An even factor is a factor that is an even number.
Some even numbers have more factors than some odd numbers and some odd numbers have more factors than some even numbers. As a group, even numbers have more factors than odd numbers.
Some even numbers have more factors than some odd numbers and some odd numbers have more factors than some even numbers. As a group, even numbers have more factors than odd numbers.
Every even number but 2. Even numbers have 2 as a factor (by definition), so higher even numbers can be separated into two factors, 2 and some other number. For example, 6 = 2 x 3.
All numbers have factors. Some factors are prime numbers, some are not.
All numbers have factors. Some factors are prime numbers. These are known as prime factors. The set of prime factors is a subset of the set of factors for any given number.
All numbers have factors. Some factors are prime numbers, some are composite numbers, one is neither. When finding the factors of a number, you find all the factors. The prime factorization is a multiplication string of just prime factors that will total the given number.
All numbers have factors. Some factors are prime numbers, some are composite numbers. A factor that is a composite number is a composite factor.
All numbers have factors. Some numbers have only two factors, the number one and the number itself. These are known as prime numbers. 7 has two factors: 1 and 7. 7 is a prime number.
There are countless numbers with more than 6 factors. 540, for example has 24 factors, and some numbers have even more.