103 LearnersLast updated on June 9th, 2025
Prime Numbers 1 to 20
Prime numbers have only two factors: 1 and the number itself. They are used in cryptography, cyber-age security, computer algorithms, and more. This topic will teach us about prime numbers from 1 to 20.
Prime Numbers 1 to 20
The numbers which are only divisible by 1 and the number itself are the prime numbers. The prime numbers between 1 and 20 are 2, 3, 5, 7, 11, 13, 17, and 19.
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Prime Numbers 1 to 20 Chart
The prime number chart is a list of prime numbers in order. This section will teach us about the prime numbers 1 to 20 chart.
List of All Prime Numbers 1 to 20
The prime numbers between 1 and 20 are the numbers which are only divisible by 1 and the number itself. The prime numbers are 2, 3, 5, 7, 11, 13, 17, and 19.
Prime Numbers - Odd Numbers
Expect 2 all the prime numbers are odd numbers, but all the odd numbers are not prime. The prime odd numbers between 1 and 20 are 3, 5, 7, 11, 13, 17, and 19.
How to Identify Prime Numbers 1 to 20
Numbers are classified into two based on the divisibility that is prime and composite numbers. There are two ways to identify the prime numbers, that is -
- By Divisibility Method
- By Prime Factorization Method
By Divisibility Method
Prime numbers are only divisible by 1 and the number itself. So, in this method, we will check whether the number is divisible by any other number or not. The number is divided by the prime numbers till the square root of the number. If the number is divisible by any other prime number, then the number is not a prime number. The number 15 is divisible by 3 and 5, so it is not a prime number.
Prime Factorization Method
In this method, the number is broken down into smaller prime numbers. The numbers are divided by the smaller prime number. If the number only breaks into 1 and the number itself, then it is a prime number. The number 33 can be broken down into 3 × 11, so it is not a prime number.
Rules for Identifying Prime Numbers 1 to 20
When talking about prime numbers, prime numbers should follow certain rules. In this section, we discuss the rules for identifying prime numbers.
Rule 1: Divisibility Check
The numbers have only two factors: those are prime numbers. So in the divisibility check, we will see whether the number is divisible by the prime number till the square root of the number.
Rule 2: Prime Factorization
Here, the number is written as the product of smaller prime numbers. If the number is a prime number, then the number cannot be broken into smaller prime numbers. So, prime factorization is only applicable for composite numbers.
Rule 3: Sieve of Eratosthenes Method
In this method, we list all the multiples of the number from 1 to 10 to find whether the number is prime or not. The numbers from 1 to 100 (or till the number required) are listed in grids. We don't consider 1 as it. Then we list the cross of all the multiples of 2 that is 4, 6, 8, 10, 12, … and encircle 2 as it is a prime number. Encircle 3 as it is prime and cross all the multiples of 3 that are 6, 9, 15, 21, ….
The process is continued till we encircle or cross all the numbers. Here the encircled are the prime numbers and the crossed are the prime numbers.
Tips and Tricks for Prime Numbers 1 to 20
When learning prime numbers use these tips and tricks to master it. Here are a few tips and tricks
- All the prime numbers are odd except 2.
- All the numbers ending in 0 are not prime numbers, because it is divisible by 2, 5 and 10.
- 5 is the only prime number that ends in 5, as other numbers ending in 5 or 0 are also divisible by 5
- Prime numbers cannot be broken down into smaller prime factors. So the prime factorization of any prime number is 11 × the given number1, that is prime factorization of 5 is 11 × 51
Common Mistakes and How to Avoid Them in Prime Numbers 1 to 20
Confusing prime and composite numbers is common among kids. So let’s discuss some common mistakes that students make when finding prime numbers from 1 to 20.
Mistake 1
Considering all prime numbers as odd
Students think that all odd numbers are prime. Because all the even numbers are divisible by 2. But there are odd numbers, which are composite numbers. That is 9, 15, 21, etc are odd numbers that are non primes.
Mistake 2
Considering 1 as a prime number
Students think that 1 is a prime number. Whereas, 1 is not a prime number nor a composite number. As it is only divisible by 1.
Mistake 3
Errors while doing the divisibility test
When checking the divisibility of a number of students may make mistakes. So students need to double-check the answer and also learn a few basic divisibility rules for smaller prime numbers.
For instance, 1047 is not a prime number, as it is divisible by 3. If the sum of the number is divisible by 3 then the number is divisible by 3. That is, 1 + 0 + 4 + 7 = 12, as 1047 is divisible by 3 as 12 is divisible by 3
Mistake 4
Thinking that large numbers cannot be prime
Students without doing proper checks think that if a number is large, then it is composite. It is wrong because there are large numbers which are prime too. Such as 100003. 100019, 100043, etc. are prime numbers.
Mistake 5
Confusing with prime numbers and prime factors
Students tend to confuse prime numbers and prime factors. To avoid this mistake they need to understand what is a prime number and prime factors. Prime numbers are the type of numbers that have only two factors: 1 and the number itself. Such as 2, 3, 5, 7, 11, … Whereas prime factors are the factors of a number which are prime.
For example, prime factors of 36 are 2 and 3.
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Prime Numbers Examples
Problem 1
Which is the largest prime number between 1 and 20?
The largest prime number between 1 and 20 is 19.
Explanation
The prime numbers between 1 and 20 are 2, 3, 5, 7, 11, 13, 17, and 19.
So, the largest prime number from 1 to 20 is 19.
Problem 2
Why is 15, not, a prime number?
15 is not a prime number as it has more than 2 factors.
Explanation
The number 15 is not a prime number as it has more than two factors.
The factors of 15 are 1, 3, 5, and 15.
Problem 3
Is 19 a prime number or not?
Yes, 19 is a prime number
Explanation
The number 19 is only divisible by 1 and 19. So it is a prime number.
Problem 4
Which of the following is not a prime number? 59, 73, 19, 91, 67
In the given number 91 is not a prime number
Explanation
The numbers 59, 73, 19, and 67 have only two factors.
Where 91 has more than two factors that is 1, 7, 13, and 91.
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FAQs on Prime Numbers 1 to 20
1.How many prime numbers are in 1 to 20?
2.Why is 1 not a prime number?
3.Which is the largest prime number between 1 and 20.
4.Which are the methods to find prime numbers?
5.List the non-prime numbers between 1 and 20?
6.How can children in Philippines use numbers in everyday life to understand Prime Numbers 1 to 20?
7.What are some fun ways kids in Philippines can practice Prime Numbers 1 to 20 with numbers?
8.What role do numbers and Prime Numbers 1 to 20 play in helping children in Philippines develop problem-solving skills?
9.How can families in Philippines create number-rich environments to improve Prime Numbers 1 to 20 skills?
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Important Glossaries for Prime Numbers 1 to 20
- Prime numbers: Any numbers which have only two factors are prime numbers. The factors of prime numbers are one and the number itself. For instance, 2, 3, 5, 7, …
- Composite numbers: If a number has more than two factors they are composite. They are 4, 6, 8, 9,
… - Factors: Factors of a number are the numbers that can evenly divide the number. The factors of 10 are 1, 2, 5, and 10.
- Odd numbers: The numbers that leave a remainder when dividing the number by two are odd. A few odd numbers are 1, 3, 5, 7, 9, …
- Even number: The numbers that leave no remainder when divided by 2 are even numbers. The even numbers are 2, 4, 6, 8, 10, …
Hiralee Lalitkumar Makwana
About the Author
Hiralee Lalitkumar Makwana has almost two years of teaching experience. She is a number ninja as she loves numbers. Her interest in numbers can be seen in the way she cracks math puzzles and hidden patterns.
Fun Fact
: She loves to read number jokes and games.
