A prime number is a number that deserve to only be divided by itself and 1 without remainders. Below we describe what precisely this means, give you a list of the prime numbers children need to understand at major school and provide you v some practice prime number questions and examples.

You are watching: Is -1 a prime number

What is a prime number?

A element number is a number greater than 1 with just two components – themselves and 1.

A prime number cannot be divided by any type of other numbers there is no leaving a remainder.

An example of a element number is 13. It can only be split by 1 and 13. Dividing a prime number by an additional number outcomes in numbers left end e.g. 13 ÷ 6 = 2 remainder 1.

15 is not an example of a prime number because it can be split by 5 and also 3 and by itself and also 1.

15 is an example of a composite number since it has much more than 2 factors.

Prime number examples

How to work out if a number is a prime number or not.


What room the prime numbers?

There space 8 element numbers under 20: 2, 3, 5, 7, 11, 13, 17 and 19.

The an initial 10 element numbers space 2, 3, 5, 7, 11, 13, 17, 19, 23, 29.

There space 25 element numbers in between 1 and also 100.

Prime number can proceed well past 100. Because that example, 21,577 is a prime number.

List of element numbers to 100

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97.

Smallest element number

2 is the smallest prime number. It likewise the only also prime number – all other also numbers can be separated by themselves, 1 and 2 in ~ least, definition they will have actually at least 3 factors.

Largest prime number

One that the most renowned mathematicians of the classic era, Euclid, taped a proof that there is no biggest prime number. However many scientists and mathematicians space still looking to find it as part of the an excellent Internet Mersenne prime Search.

Thelargest well-known prime number(as of November2020) is282,589,933− 1, a number which has 24,862,048 digits once written in base 10. Prior to then the largest well-known prime number to be 277,232,917-1, having actually 23,249,425 digits.

By the moment you check out this it may be also larger, yet you have the right to follow its development on Wikipedia.

Common FAQs about prime numbers

Is 1 a prime number

1 is no a prime number since it has only one factor, namely 1. Prime numbers have to have specifically two factors

Is 51 a prime number?

51 is not a element number since it can be split by 3 and also 17, as well as by itself and also 1. In other words it has four factors.

Download cost-free Now!

Prime numbers in primary school

Prime numbers room not presented in the UK till Year 5.

According come the national Curriculum, Year 5 kids should be taught to

“know and use the vocabulary of prime numbers, element factors and composite (non-prime) numbers to establish whether a number approximately 100 is prime and recall prime numbers approximately 19.”

In Year 6, youngsters should it is in able to“identify common factors, common multiples and prime numbers”.

How are prime numbers supplied in the actual world?

One of the most important uses for prime numbers is in cyber security – making information shared over the web safer.

In order to encrypt (make secure) things choose credit map details, clinical records, even some message services prefer WhatsApp, software engineers make algorithms using prime numbers.

By multiplying 2 very large prime numbers with each other (some providers use element numbers that are hundreds of digits long!), we produce an even larger number whose original components (the 2 very large prime numbers) are only recognized to us. Us then usage this also larger number to encrypt ours information.

If anyone else desires to uncover what information we space sending, they have to find out what ours original determinants were. V prime numbers as lengthy as the people we have used, it might take them year or even decades of continuous trial and error before they discover even one. This ensures our details is maintained safe.

Wondering about how to explain other crucial maths vocabulary to your children? inspect out our main Maths Dictionary, or shot these primary maths terms:

Prime number questions

1) A square number and also a element number have actually a full of 22. What space the two numbers?

A: 9 and also 13

2) Emma think of 2 prime numbers. She to add the 2 numbers together. She answer is 36. Create all the possible pairs of element numbers Emma could be reasoning of.

A: 3 and also 33; 5 and also 31; 7 and also 29; 13 and also 23; 17 and 19

3) one the two prime number – 29, 59, 39, 69, 29

A: 29 and also 59

4) create the three prime numbers which main point to make 231.

A: 3 x 7 x 11

CHALLENGE QUESTION: Chen choose a element number. The multiplies the by 10 and then rounds it to the nearest hundred. His price is 400. Write all the feasible prime numbers Chen might have chosen.

A: 37, 41 or 43.

Third space Learning’s virtual Maths Hub contains hundreds the maths sources for main school teachers and parents to use in school and also at home. Registration for the totally free maths resources is quick, simple and available for all staff at your school. To accessibility the premium resources, your college will need a premium Maths Hub subscription. Alternatively, accessibility to all premium resources is included at no extr cost for schools signed up to our online tuition for maths.

See more: How Long Does Salsa Last After Opening, Does Salsa Go Bad After Expiration Date

Prime number worksheets

Prime number videos

Online 1-to-1 maths lessons trusted by schools and also teachersEvery week Third room Learning’s maths professional tutors assistance thousands of main school youngsters with weekly virtual 1-to-1 lessons and maths interventions. Due to the fact that 2013 we’ve assisted over 100,000 children become more confident, maybe mathematicians. Learn more or inquiry a personalised quote to speak to us about your needs and how we have the right to help.

Our online tuition for maths programme provides every son with your own skilled one to one maths tutor