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Broad Topics > Numbers and the Number System > Prime numbers

### Black Box

##### Stage: 5 Challenge Level:

This black box reveals random values of some important, but unusual, mathematical functions. Can you deduce the purpose of the black box?

### Various Venns

##### Stage: 2 Challenge Level:

Use the interactivities to complete these Venn diagrams.

### Factors and Multiples Game

##### Stage: 2, 3 and 4 Challenge Level:

A game in which players take it in turns to choose a number. Can you block your opponent?

### Factors and Multiples Puzzle

##### Stage: 3 Challenge Level:

Using your knowledge of the properties of numbers, can you fill all the squares on the board?

### Stars

##### Stage: 3 Challenge Level:

Can you find a relationship between the number of dots on the circle and the number of steps that will ensure that all points are hit?

### Two Primes Make One Square

##### Stage: 2 Challenge Level:

Can you make square numbers by adding two prime numbers together?

### Factor Lines

##### Stage: 2 and 3 Challenge Level:

Arrange the four number cards on the grid, according to the rules, to make a diagonal, vertical or horizontal line.

### Why 24?

##### Stage: 4 Challenge Level:

Take any prime number greater than 3 , square it and subtract one. Working on the building blocks will help you to explain what is special about your results.

### Round and Round the Circle

##### Stage: 2 Challenge Level:

What happens if you join every second point on this circle? How about every third point? Try with different steps and see if you can predict what will happen.

### Factors and Multiples Game for Two

##### Stage: 2 Challenge Level:

Factors and Multiples game for an adult and child. How can you make sure you win this game?

### Sieve of Eratosthenes

##### Stage: 3 Challenge Level:

Follow this recipe for sieving numbers and see what interesting patterns emerge.

### Weekly Challenge 44: Prime Counter

##### Stage: 5 Challenge Level:

A weekly challenge concerning prime numbers.

### Prime Sequences

##### Stage: 5 Challenge Level:

This group tasks allows you to search for arithmetic progressions in the prime numbers. How many of the challenges will you discover for yourself?

### Coins

##### Stage: 3 Challenge Level:

A man has 5 coins in his pocket. Given the clues, can you work out what the coins are?

### Numbers as Shapes

##### Stage: 1 Challenge Level:

Use cubes to continue making the numbers from 7 to 20. Are they sticks, rectangles or squares?

### An Introduction to Proof by Contradiction

##### Stage: 4 and 5

An introduction to proof by contradiction, a powerful method of mathematical proof.

### Different by One

##### Stage: 4 Challenge Level:

Make a line of green and a line of yellow rods so that the lines differ in length by one (a white rod)

### Bubble Trouble

##### Stage: 1 Challenge Level:

Can you find just the right bubbles to hold your number?

### Factorial Fun

##### Stage: 5 Challenge Level:

How many divisors does factorial n (n!) have?

### A Conversation Piece

##### Stage: 2 Challenge Level:

Take the number 6 469 693 230 and divide it by the first ten prime numbers and you'll find the most beautiful, most magic of all numbers. What is it?

### Code Breaker

##### Stage: 2 Challenge Level:

This problem is based on a code using two different prime numbers less than 10. You'll need to multiply them together and shift the alphabet forwards by the result. Can you decipher the code?

### Penta Primes

##### Stage: 2 Challenge Level:

Using all ten cards from 0 to 9, rearrange them to make five prime numbers. Can you find any other ways of doing it?

### Tom's Number

##### Stage: 2 Challenge Level:

Work out Tom's number from the answers he gives his friend. He will only answer 'yes' or 'no'.

### Strange Numbers

##### Stage: 3 Challenge Level:

All strange numbers are prime. Every one digit prime number is strange and a number of two or more digits is strange if and only if so are the two numbers obtained from it by omitting either. . . .

### What's Left?

##### Stage: 1 Challenge Level:

Use this grid to shade the numbers in the way described. Which numbers do you have left? Do you know what they are called?

### Prompt Cards

##### Stage: 2 Challenge Level:

These two group activities use mathematical reasoning - one is numerical, one geometric.