WorkedMathGlossary

Factors of 28

The factors of 28 are 1, 2, 4, 7, 14, 28. No, 28 is a composite number. Its prime factorization is 2^2 × 7.

Factors of 28
1, 2, 4, 7, 14, 28
6 factors
Prime or Composite
Composite
Perfect Square
No
Prime Factorization
2^2 × 7
Sum of Factors
56 (28 without 28 itself)

Factor pairs of 28

Every factor has a partner that multiplies with it to give 28. Listing pairs from the outside in is the fastest way to find all the factors: once the two numbers in a pair meet in the middle, you have them all.

PairCheck
1 and 281 × 28 = 28
2 and 142 × 14 = 28
4 and 74 × 7 = 28

Prime factorization of 28, step by step

Divide by the smallest prime that goes in evenly, then repeat on the result until you reach 1. The divisors you used are the prime factors.

StepDivideResult
128 ÷ 214
214 ÷ 27
37 ÷ 71

So 28 = 2 × 2 × 7, written compactly as 2^2 × 7.

Divisibility checks for 28

The quick rules a student uses before dividing, applied to 28:

Divisible byRuleFor 28Result
2last digit is evenlast digit 8yes
3digit sum divisible by 3digits add to 10no
4last two digits divisible by 428 ÷ 4yes
5last digit is 0 or 5last digit 8no
6divisible by both 2 and 3even, digit sum 10no
8last three digits divisible by 828 ÷ 8no
9digit sum divisible by 9digits add to 10no
10last digit is 0last digit 8no

Frequently Asked Questions

What are the factors of 28?

The factors of 28 are 1, 2, 4, 7, 14, 28.

Is 28 a prime number?

No, 28 is a composite number. Its prime factorization is 2^2 × 7.

How many factors does 28 have?

28 has 6 factors. You can get that count from the prime factorization without listing them: add 1 to each exponent in 2^2 × 7 and multiply -- (2+1) × (1+1) = 6.

Is 28 even or odd?

28 is even (2 is one of its factors).

What is the sum of the factors of 28?

1 + 2 + 4 + 7 + 14 + 28 = 56. Leaving out 28 itself, the proper factors add to 28 -- equal to 28, which makes 28 a perfect number.

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