Is 1215 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 1215 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 1215 has more than two factors, it is not a prime number. A few methods are used to distinguish between prime and composite numbers. A few methods are:

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 1215 is prime or composite.

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

Step 2: Divide 1215 by 2. It is not divisible by 2, so 2 is not a factor of 1215.

Step 3: Divide 1215 by 3. It is divisible by 3, so 3 is a factor of 1215.

Step 4: You can simplify checking divisors up to 1215 by finding the root value. We then need to check divisors up to the root value.

Step 5: When we divide 1215 by 3, 5, 9, 15, etc., it is divisible by several numbers.

Since 1215 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: The number in the one's place value is 5. Since 5 is odd, 1215 is not divisible by 2.

Divisibility by 3: The sum of the digits in the number 1215 is 9. Since 9 is divisible by 3, 1215 is also divisible by 3.

Divisibility by 5: The unit’s place digit is 5. Therefore, 1215 is divisible by 5.

Divisibility by 11: Alternating sum of the digits (1 - 2 + 1 - 5 = -5) is not divisible by 11, so 1215 is not divisible by 11. Since 1215 is divisible by numbers other than 1 and itself, 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 numbers in a sequence, like 1 to 1000.

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 from 1 to 1000.

1215 is not present in the list of prime numbers, so 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 1215 as 3 × 405.

Step 2: In 3 × 405, 405 is a composite number. Further, break the 405 into 3 × 135.

Step 3: Break down 135 into 3 × 45, and then 45 into 3 × 15, and finally 15 into 3 × 5.

Step 4: Now we get the product consisting of only prime numbers.

Hence, the prime factorization of 1215 is 3 × 3 × 3 × 3 × 5.

• 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 numbers: Natural numbers greater than 1 that are divisible only by 1 and themselves.

• Factors: The numbers that divide the number exactly without leaving a remainder are called factors.

• Divisibility rules: A set of shortcuts that help determine whether a number is divisible by another without performing the actual division.

• Prime factorization: The process of expressing a number as a product of its prime factors.