How Many Prime Numbers are There Between 1 to 20

Introduction

There are 8 prime numbers between 1 to 20 (2,3,5,7,11,13,17,19). Prime numbers are natural numbers that are divisible by 1 and the number itself alone. In other terms, prime numbers are positive integers greater than one that only have the number itself and the number 1 as its factors.Examples are 2,3,5,7 etc. Note that 1 is neither a prime number nor a composite. Apart from 1, the other numbers can all be categorised as prime and composite numbers. Except for 2, which is the smallest even prime number otherwise all prime numbers are odd.(odd means which are not divisible by 2 and even means which are divisible by 2)

Background on Prime Numbers

Since ancient times, people have been curious about prime numbers. Mathematicians are still searching for prime numbers with enigmatic qualities today. There are infinitely many prime numbers, according to a theorem put forward by Euclid.

Do you know every prime number between 1 and 100? Did you verify that each number may be divided into smaller numbers? One of the finest scientists, Eratosthenes, lived a few decades after Euclid. He created a clever method to ascertain all prime numbers up to a specific quantity. The Sieve of Eratosthenes is the name of this technique.

Easy Ways to Find Prime Numbers

There are several ways to tell if a number is prime or not. The factorization method is the most effective approach for locating prime integers. A number's factors can be discovered by factorization, making it simple to spot a prime number.

How to find prime numbers by use of factorization

The best method for discovering prime numbers is factorization. The factorization approach involves the following steps:

Step 1: Determine the provided number's factors first.

Step 2: Determine how many factors that number has.

Step 3: If factors count is more than two then it is not a prime number

Example: Now, 18 can be written as 2\times 3\times 3 Therefore, 1, 2, 3, 6, 9, and 18 are the factors of 18. 18 is a composite number rather than a prime number since it has more than two factors.

Now let's use the number 17 as an example 1\times 17 is the prime factorization of 17 Here, you can see that the number 17 has two factors so from above definition we can say it is prime numbers

Now let's use the number 13 as an example 1\times 13 is the prime factorization of 13 Here, you can see that the number 13 has two factors hence it is also a prime number

Now let's use the number 7 as an example. 1\times 7 is the prime factorization of 7 Here, you can see that the number 7 has two factors so 7 is also a prime number

Characteristics of Prime Numbers:

• Prime numbers has exactly two factors (1 and number itself)

• 2 is only even prime number

• Every pair of prime numbers is always a co-prime.

• Every natural number greater than 1 can be expressed as a product of prime numbers and this is known as prime factorization

• Numbers that finish in 0, 2, 4, 6, or 8 are not prime numbers.

• Calculate the number's digit sum and if the sum is divisible by three then we can say that the given number is not a prime number

List of Prime Numbers