Is 55 a Prime Number?

We could find that a number is prime if it has 2 factors only, 1 and the number itself. 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

Let's see how each of these tests helps us in finding prime numbers.

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.

• Divisors of 55: 1,5,11 and 55.

• Number of divisors: 4

We can see that number 55 has four divisors. And we see that it doesn’t fulfill the criteria needed for a prime number. So it is not a prime number.
 

Let's check 55 is divisible by how many numbers. If 55 is divisible by even one of the numbers, then it will not be a prime number. Let's check the divisibility with 2,3,5 and 7. 

• That is, any number ending in an even number is divisible by 2. And 55 ends with an odd number. Actually, 5 is not a multiple of 2, so it is an odd number. So that 55 will not be divisible by 2 and it is not a prime number.

• The sum of the digits of the number 55 is 10. Now, in order to be divisible by 3, the sum of the digits needs to be a multiple of 3. Since 10 is not a multiple of 3. Therefore, 55 is not divisible by 3.

• 55 does end in 0 or 5. To be divisible by 5 a number should end in 0 or 5. So, 55 can be divided by 5.

• We know how to see whether 55 is divisible by 7. Let's simply glance at the last digit, which is 5. We have doubled that 5 to get 10, then subtract the other digit, which is 5. So, we do 10 – 5 = 5. Since 5 is not a multiple of 7, it means that 55 is not divisible by 7.

We see that 55 is exactly divisible by one of the above numbers. Hence, 55 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 55 does not appear here. So, it is not a prime number.

This method is used to break huge numbers into smaller numbers and find the prime factors of the given number.

We know the prime factorization of 55 is 13×5. Since there are more than two factors for 55, we can not call 55 a prime number.
 

• Divisors:  A number that divides another number and leaves no remainder is called divisors.For example, 4/2=2. Here, 2 is a divisor, as it divides 4 exactly and leaves no remainder.

• Composite number: The number which possesses more than 1 factor is named as composite number. Like, example- 18 is factored into 2×32, thus it is a composite number.

• Natural number: All the numbers that are positive and whole numbers form 1.

• Multiple: The product of 2 number is called a multiple. For example, 6 and 9 are multiples of 3.