Is 778 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 778 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 778 has more than two factors, it is not a prime number. A few methods are used to distinguish between prime and composite numbers. Some methods are:

• Counting Divisors Method
   
• Divisibility Test
   
• Prime Number Chart
   
• 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 numbers as prime or composite. 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 778 is prime or composite.

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

Step 2: Divide 778 by 2. It is divisible by 2, so 2 is a factor of 778.

Step 3: Divide 778 by 3. It is not divisible by 3, so 3 is not a factor of 778.

Step 4: You can simplify checking divisors up to 778 by finding the root value. We then need to only check divisors up to the root value.

Step 5: When we divide 778 by 2, 389, and other numbers, it is divisible by 2 and 389.

Since 778 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 ones' place value is 8. Eight is an even number, which means that 778 is divisible by 2.

Divisibility by 3: The sum of the digits in the number 778 is 22. Since 22 is not divisible by 3, 778 is also not divisible by 3.

Divisibility by 5: The unit’s place digit is 8. Therefore, 778 is not divisible by 5.

Divisibility by 7: The last digit in 778 is 8. To check divisibility by 7, double the last digit (8 × 2 = 16). Then, subtract it from the rest of the number (77 - 16 = 61). Since 61 is not divisible by 7, 778 is also not divisible by 7.

Divisibility by 11: In 778, the sum of the digits in odd positions is 14, and the sum of the digits in even positions is 7. The difference is 7, which means that 778 is not divisible by 11.

Since 778 is divisible only by 2 and 389, 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 from 1 to 1000.

778 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 778 as 2 × 389.

Step 2: In 2 × 389, 389 is a prime number. Further factorization is not required.

Step 3: Now we get the product consisting of only prime numbers.

Hence, the prime factorization of 778 is 2 × 389.

• 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 a product of its prime factors. For example, the prime factorization of 28 is 2 × 2 × 7.
   
• Divisibility rules: A set of rules that help determine if one number is divisible by another without performing the 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 works by iteratively marking the multiples of each prime number starting from 2.
   
• Co-prime numbers: Two numbers are co-prime if their greatest common divisor is 1. For example, 8 and 15 are co-prime because their only common factor is 1.