Factors of 28
The factors of 28 are 1, 2, 4, 7, 14, and 28. In total, 28 has 6 factors. Its prime factorization is 2² × 7, and the sum of all its factors is 56. 28 is a perfect number — its proper factors add up to exactly 28.
All factors of 28
Here are all 6 factors of 28, listed from smallest to largest.
Factor pairs of 28
These 3 pairs of whole numbers each multiply to give 28.
Prime factorization of 28
Dividing 28 by the smallest prime at each step gives its prime factorization:
The distinct prime factors of 28 are 2, 7. To factorize any other number, use the prime factorization calculator.
Factor tree of 28
A factor tree shows the same prime factorization visually. Each composite branch splits until every endpoint is a prime number.
Properties of 28
| Number of factors | 6 |
|---|---|
| Sum of factors | 56 |
| Sum of proper factors | 28 |
| Prime factorization | 2² × 7 |
| Prime or composite? | Composite |
| Even or odd? | Even |
| Perfect square? | No |
| Perfect cube? | No |
| Classification | Perfect |
What makes 28 interesting
- 28 is a composite number, meaning it has more than two factors. It can be written as a product of smaller whole numbers in 3 different ways.
- 28 is a perfect number — a rare classification. Its proper factors (1, 2, 4, 7, 14) add up to exactly 28. Only 51 perfect numbers are known.
- 28 is a triangular number — it is the sum of the first 7 whole numbers (1 + 2 + … + 7 = 28).
How to find the factors of 28 yourself
Divide 28 by each whole number starting from 1. Whenever the division leaves no remainder, both the divisor and the quotient are factors. You only need to test up to √28 ≈ 5.29, because every factor above that pairs with one below it.
Reading both columns gives every factor: 1, 2, 4, 7, 14, 28. The factor calculator does this automatically for any number.
Related numbers
Numbers mathematically connected to 28.
Frequently asked questions about 28
What are the factors of 28?
Is 28 a prime number?
What is the prime factorization of 28?
What two numbers multiply to give 28?
What is the sum of the factors of 28?
Is 28 a perfect square?
What is the largest factor of 28 other than itself?
How many factors does 28 have?
Explore more
Try another number in the factor calculator, break 28 down further with the prime factorization calculator, or compare 28 with another number using the GCF calculator and LCM calculator. For divisor counts and sums, see the divisor calculator.