
This is an interactivity in which you have to sort into the correct order the steps in the proof of the formula for the sum of a geometric series.

Can you see how this picture illustrates the formula for the sum of the first six cube numbers?
Yatir from Israel wrote this article on numbers that can be written as 2^n-n where n is a positive integer.

Make a conjecture about the sum of the squares of the odd positive integers and prove your conjecture.
Yatir from Israel describes his method for summing a series of triangle numbers.
This article by Alex Goodwin, age 18 of Madras College, St Andrews describes how to find the sum of 1 + 22 + 333 + 4444 + ... to n terms.

Prove that k.k! = (k+1)! - k! and sum the series 1.1! + 2.2! + 3.3! +...+n.n!

Bricks are 20cm long and 10cm high. How high could an arch be built without mortar on a flat horizontal surface, to overhang by 1 metre? How big an overhang is it possible to make like this?

Prove that the sum of the reciprocals of the first n triangular numbers is approximately equal to 2 when n is large and tends to 2 as n tends to infinity.

Find S_r = 1^r + 2^r + 3^r + ... + n^r where r is any fixed positive integer in terms of S_1, S_2, ... S_{r-1}.

Find relationships between the polynomials a, b and c which are polynomials in n giving the sums of the first n natural numbers, squares and cubes respectively.

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.

Each week a company produces X units and sells p per cent of its stock. How should the company plan its warehouse space?

By tossing a coin one of three princes is chosen to be the next King of Randomia. Does each prince have an equal chance of taking the throne?

What does Pythagoras' Theorem tell you about these angles: 90°, (45+x)° and (45-x)° in a triangle? Find sin^2 1° + sin^2 2° + ... + sin^2 359 ° + sin^2 360°.
This article gives an introduction to mathematical induction, a powerful method of mathematical proof.

What is the sum of: 6 + 66 + 666 + 6666 ............+ 666666666...6 where there are n sixes in the last term?

Is it true that a large integer m can be taken such that: 1 + 1/2 + 1/3 + ... +1/m > 100 ?