# Is 1 a Prime Number?

**Prime Number Posters** – Is one a prime number? A simple test to see if a number is prime.

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**Is 1 a Prime Number?**

**Is 1 a Prime Number?**

**No! One is NOT a prime number!**

I usually try to introduce the concept of 1 not being prime by examining the mathematical definition… very closely.

**‘For a number to be prime it must have TWO distinct (different) factors’. Ham up the word TWO. Use a funny voice.**

In 1’s case, its factors are 1 and 1.

**For a number to be prime it must be able to be divided by itself AND 1. Ham up the word AND. Use a funny voice.**

In the case of 1 ‘itself ‘ **IS** one.

This poster can then be added to your Math Vocabulary Display as a form of Math Help or reference material 🙂

**What is a Prime Number?**

Here is a simple test you can do to work out if a number is prime. e.g. Is 11 prime? Is 21 prime? etc

Use blocks to see if the poster below helps your students identify prime numbers.

**You might also like to have a look at…**

– What is a prime number?

– Is two a prime number?

– a list of prime numbers

– The technical reason why 1 is not prime

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