Is 867 a Prime Number?

There are two types of numbers, mostly — Prime numbers and composite numbers, depending on the number of factors. A prime number is a natural number that is divisible only by 1 and itself. For example, 3 is a prime number because it is divisible by 1 and itself.

A composite number is a positive number that is divisible by more than two numbers. For example, 6 is divisible by 1, 2, 3, and 6, making it a composite number. Prime numbers follow a few properties like: 

• Prime numbers are positive numbers always greater than 1. -
• 2 is the only even prime number. -
• They have only two factors: 1 and the number itself. -
• Any two distinct prime numbers are co-prime numbers because they have only one common factor, which is 1.
• As 867 has more than two factors, it is not a prime number.

The characteristic of a prime number is that it has only two divisors: 1 and itself. Since 867 has more than two factors, it is not a prime number. A few methods are used to distinguish between prime and composite numbers, such as: -

1. Counting Divisors Method 
2. Divisibility Test 
3. Prime Number Chart 
4. Prime Factorization

The method in which we count the number of divisors to categorize the numbers as prime or composite is called the counting divisors method. Based on the count of the divisors, we categorize prime and composite numbers

• If there is a total count of only 2 divisors, then the number would be prime. 
• If the count is more than 2, then the number is composite. Let’s check whether 867 is prime or composite.

Step 1: All numbers are divisible by 1 and itself.

Step 2: Divide 867 by 2. It is not divisible by 2, as 867 is odd.

Step 3: Divide 867 by 3. It is divisible by 3, so 3 is a factor of 867.

Step 4: You can simplify checking divisors up to 867 by finding the root value. We then need to only check divisors up to the root value.

Step 5: When we divide 867 by 3, it is divisible, confirming it has more than 2 divisors.

Since 867 has more than 2 divisors, it is a composite number.

We use a set of rules to check whether a number is divisible by another number completely or not. It is called the Divisibility Test Method.

Divisibility by 2: 867 is an odd number, so it is not divisible by 2. -

Divisibility by 3: The sum of the digits in the number 867 is 21 (8 + 6 + 7), which is divisible by 3. Therefore, 867 is divisible by 3. -

Divisibility by 5: The unit’s place digit is 7. Therefore, 867 is not divisible by 5. -

Divisibility by 7: Calculating gives 867 ÷ 7 = 123, which is an integer. Therefore, 867 is divisible by 7. -

Divisibility by 11: The alternating sum of the digits in 867 is 5 (8 - 6 + 7), which is not divisible by 11. Therefore, 867 is not divisible by 11.

Since 867 is divisible by 3 and 7, it has more than two factors. Therefore, it is a composite number.

The prime number chart is a tool created by using a method called “The Sieve of Eratosthenes.” In this method, we follow the following steps.

Step 1: Write 1 to 1000 in rows and columns.

Step 2: Leave 1 without coloring or crossing, as it is neither prime nor composite. Step 3: Mark 2 because it is a prime number and cross out all the multiples of 2.

Step 4: Mark 3 because it is a prime number and cross out all the multiples of 3.

Step 5: Repeat this process until you reach the table consisting of marked and crossed boxes, except 1. Through this process, we will have a list of prime numbers. If 867 is not present in the list of prime numbers, it is a composite number.

Prime factorization is a process of breaking down a number into prime factors. Then multiply those factors to obtain the original number.

Step 1: We can write 867 as 3 × 289.

Step 2: In 3 × 289, 289 is a composite number, further break down 289 into 17 × 17.

Step 3: Now we get the product consisting of only prime numbers. Hence, the prime factorization of 867 is 3 × 17 × 17.

• Composite numbers: Natural numbers greater than 1 that are divisible by more than 2 numbers are called composite numbers. For example, 12 is a composite number because 12 is divisible by 1, 2, 3, 4, 6, and 12.

• Prime factorization: The process of expressing a number as the product of its prime factors. For example, the prime factorization of 18 is 2 × 3 × 3. 

• Divisibility test: A method to determine if one number is divisible by another without performing division. For example, a number is divisible by 3 if the sum of its digits is divisible by 3. 

• Sieve of Eratosthenes: An ancient algorithm used to find all prime numbers up to a specified integer. It systematically eliminates the multiples of each prime number starting from 2. 

• Natural numbers: The set of positive integers starting from 1, used for counting and ordering.