How many positive integers are factors of 21. How to find all positive factors of 21? Is 21 a prime or a composit number? How to find factors of 21.
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1 Answer

The factors of the number 21 are: 21, 7, 3, 1

The square root of 21 rounded up to the nearest integer is 5. This is the limit to test our divisions because any number greater than 5 times 5 is greater than 21. So, we stop at 5.

Let's test the values 1 through 5 for division into 21.

  • 21/1 = 21. Remainder = 0. So, 21 and 1 are factors.
  • 21/2 = 10. Remainder = 1. So, 10 isn't a factor.
  • 21/3 = 7. Remainder = 0. So, 7 and 3 are factors.
  • 21/4 = 5. Remainder = 1. So, 5 isn't a factor.
  • 21/5 = 4. Remainder = 1. So, 4 isn't a factor.

Factors of a number n are numbers that can divide n without remainder, ie, remainder = 0. So, choosing only the numbers that meet this criteria from the list above, we find that the numbers which divide 21 (including 21) with no remainder are: 21, 7, 3, 1.

So, the factors of the number 21 are: 21, 7, 3, 1.

A composite number has more than two factors. A prime number has only two factors: 1 and itself. The number 1 is neither prime nor composite.

Because the number 21 has 4 factors, it is termed a composite number in mathematics.

As 21 is a composite number, we can factorize it, ie, express it in prime Factors as follows.

By factorizing 21 we get: 21 = 3 * 7.

Ie, 21 can be expressed as a product (factor string) of prime numbers (3 * 7).

answered by expert