How many different colours of paint would be needed to paint these pictures by numbers?

Yatir from Israel describes his method for summing a series of triangle numbers.

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

Make a conjecture about the sum of the squares of the odd positive integers. Can you prove it?

Change the squares in this diagram and spot the property that stays the same for the triangles. Explain...

A and B are two fixed points on a circle and RS is a variable diamater. What is the locus of the intersection P of AR and BS?

Drawing a triangle is not always as easy as you might think!

Find the sum, f(n), of the first n terms of the sequence: 0, 1, 1, 2, 2, 3, 3........p, p, p +1, p + 1,..... Prove that f(a + b) - f(a - b) = ab.

If a number N is expressed in binary by using only 'ones,' what can you say about its square (in binary)?

Points D, E and F are on the the sides of triangle ABC. Circumcircles are drawn to the triangles ADE, BEF and CFD respectively. What do you notice about these three circumcircles?

The points P, Q, R and S are the midpoints of the edges of a non-convex quadrilateral.What do you notice about the quadrilateral PQRS and its area?

Beautiful mathematics. Two 18 year old students gave eight different proofs of one result then generalised it from the 3 by 1 case to the n by 1 case and proved the general result.

Yatir from Israel wrote this article on numbers that can be written as $ 2^n-n $ where n is a positive integer.

Four rods of equal length are hinged at their endpoints to form a rhombus. The diagonals meet at X. One edge is fixed, the opposite edge is allowed to move in the plane. Describe the locus of. . . .

Can you find the values at the vertices when you know the values on the edges of these multiplication arithmagons?

Explore the relationship between quadratic functions and their graphs.

For which values of n is the Fibonacci number fn even? Which Fibonnaci numbers are divisible by 3?

Join in this ongoing research. Build squares on the sides of a triangle, join the outer vertices forming hexagons, build further rings of squares and quadrilaterals, investigate.

A point moves on a line segment. A function depends on the position of the point. Where do you expect the point to be for a minimum of this function to occur.

What have Fibonacci numbers got to do with Pythagorean triples?

Find the maximum value of n to the power 1/n and prove that it is a maximum.

Make and prove a conjecture about the cyclic quadrilateral inscribed in a circle of radius r that has the maximum perimeter and the maximum area.

Alison has created two mappings. Can you figure out what they do? What questions do they prompt you to ask?

Have a go at creating these images based on circles. What do you notice about the areas of the different sections?

Two semicircle sit on the diameter of a semicircle centre O of twice their radius. Lines through O divide the perimeter into two parts. What can you say about the lengths of these two parts?

Find out about Magic Squares in this article written for students. Why are they magic?!

What have Fibonacci numbers to do with solutions of the quadratic equation x^2 - x - 1 = 0 ?

Investigate sequences given by $a_n = \frac{1+a_{n-1}}{a_{n-2}}$ for different choices of the first two terms. Make a conjecture about the behaviour of these sequences. Can you prove your conjecture?

Evaluate these powers of 67. What do you notice? Can you convince someone what the answer would be to (a million sixes followed by a 7) squared?

Can you find some Pythagorean Triples where the two smaller numbers differ by 1?

Make and prove a conjecture about the value of the product of the Fibonacci numbers $F_{n+1}F_{n-1}$.

A serious but easily readable discussion of proof in mathematics with some amusing stories and some interesting examples.

Many numbers can be expressed as the difference of two perfect squares. What do you notice about the numbers you CANNOT make?

Here is a machine with four coloured lights. Can you make two lights switch on at once? Three lights? All four lights?

Steve has created two mappings. Can you figure out what they do? What questions do they prompt you to ask?

A sequence of polynomials starts 0, 1 and each poly is given by combining the two polys in the sequence just before it. Investigate and prove results about the roots of the polys.

The points P, Q, R and S are the midpoints of the edges of a convex quadrilateral. What do you notice about the quadrilateral PQRS as the convex quadrilateral changes?

Can you find a rule which connects consecutive triangular numbers?

Make a conjecture about the curved track taken by the complex roots of a quadratic equation and use complex conjugates to prove your conjecture.

Show that all pentagonal numbers are one third of a triangular number.

Show that for any triangle it is always possible to construct 3 touching circles with centres at the vertices. Is it possible to construct touching circles centred at the vertices of any polygon?

A polite number can be written as the sum of two or more consecutive positive integers. Find the consecutive sums giving the polite numbers 544 and 424. What characterizes impolite numbers?

Problem solving is at the heart of the NRICH site. All the problems give learners opportunities to learn, develop or use mathematical concepts and skills. Read here for more information.

What happens to the perimeter of triangle ABC as the two smaller circles change size and roll around inside the bigger circle?

Janine noticed, while studying some cube numbers, that if you take three consecutive whole numbers and multiply them together and then add the middle number of the three, you get the middle number. . . .

Take any parallelogram and draw squares on the sides of the parallelogram. What can you prove about the quadrilateral formed by joining the centres of these squares?

In 15 years' time my age will be the square of my age 15 years ago. Can you work out my age, and when I had other special birthdays?

Take a number, add its digits then multiply the digits together, then multiply these two results. If you get the same number it is an SP number.