Is 100 a Prime Number?

100 is not a prime number. But according to what we are saying, why is it not a prime number? Let's understand that, firstly, the number set is of two parts:

• Prime number

• composite numbers

And using one of the methods we're going to introduce you to, we will find that indeed 100 is not a prime.

We could find that a number is prime if it has 2 factors only, 1 and the number itself, and only 2 divisors. It means that a number, not satisfying these conditions, cannot be a prime number.

However, there are pretty simple methods to determine whether a number is prime or not:

• Count Divisor Method

• Divisibility Test

• Prime Number Table

• Prime Factorization
   

The name implies: We’re counting how many divisors a given number has, and then saying that number is prime. It is easy to learn. With that said, let’s see what steps are there in this method.

• First is to count how many the number holds in divisors.

• We can then see that 100 has more than 2 divisors: 1,2,4,5,10,20,25,50 and 100.

We can see that number 100 has 9 divisors. Thus, we see that it doesn’t fulfill the criteria needed for a prime number. And so it is not a prime number.
 

In this case, we'll see if 100 can be divided into any other number. Now if it gets divided then that is not a prime number. So let’s check for 2,3,5 and 7.

• Since 100 is an even number, we can say that 100 is divisible by 2.

• Since the sum of the digits is 1, 1 is not divisible by 3 as 1 is not a multiple of 3. 

• 100 is ending with a 0 or 5. Therefore, it is divisible by 5.

• To see if 100 is divisible by 7, we can use a simple trick. First, we look at the last digit, which is 0. We double that 0 (0 × 2 = 0) and then subtract it from the other digit, which is 1. So, we do 1 – 0 = 1. Since 1 is not a multiple of 7, that means 100 isn’t divisible by 7.

We know 100 can be divided by two of the above-mentioned numbers, therefore it is not a prime number.
 

Here, we will be using a chart that will contain all the prime numbers between 1 and 100. If the given number appears in the list, it is not a prime number. 
 

We can see that 100 does not appear here. So, it is not a prime number.

We use this method of breaking large numbers into small numbers, then checking the factors. It works only for composite numbers. 

The factors of 100 are 2 and 5. Since there are more than two factors for 100, we can not title 100 a prime number.

• Composite number- The number which possesses more than 1 factor is named as composite number. Like, example- 18 is factorized into 2x32 thus it is a composite number.

• Factor- A number, if multiplied with another number, gives us the required number. Example, 7x2=14, 7x3=21. In that, 2 and 3 are factors.

• Co-prime Numbers- These numbers have a GCF of 1. 

• Prime Number Chart- A list of prime numbers, often used to quickly determine if a number is prime by checking if it appears in the list.