There are **33** NRICH Mathematical resources connected to **Algorithms**, you may find related items under Decision Mathematics and Combinatorics.

Is the regularity shown in this encoded message noise or structure?

Watch our videos of multiplication methods that you may not have met before. Can you make sense of them?

Using the digits 1 to 9, the number 4396 can be written as the product of two numbers. Can you find the factors?

How can you quickly sort a suit of cards in order from Ace to King?

Can you crack these very difficult challenge ciphers? How might you systematise the cracking of unknown ciphers?

How would you judge a competition to draw a freehand square?

Can you interpret this algorithm to determine the day on which you were born?

This article explains the concepts involved in scientific mathematical computing. It will be very useful and interesting to anyone interested in computer programming or mathematics.

It's like 'Peaches Today, Peaches Tomorrow' but interestingly generalized.

What day of the week were you born on? Do you know? Here's a way to find out.

However did we manage before calculators? Is there an efficient way to do a square root if you have to do the work yourself?

Can you think like a computer and work out what this flow diagram does?

Imagine a strip with a mark somewhere along it. Fold it in the middle so that the bottom reaches back to the top. Stetch it out to match the original length. Now where's the mark?

Read this article to find out the mathematical method for working out what day of the week each particular date fell on back as far as 1700.

Scheduling games is a little more challenging than one might desire. Here are some tournament formats that sport schedulers use.

When in 1821 Charles Babbage invented the `Difference Engine' it was intended to take over the work of making mathematical tables by the techniques described in this article.

When the number x 1 x x x is multiplied by 417 this gives the answer 9 x x x 0 5 7. Find the missing digits, each of which is represented by an "x" .

This addition sum uses all ten digits 0, 1, 2...9 exactly once. Find the sum and show that the one you give is the only possibility.

The number 10112359550561797752808988764044943820224719 is called a 'slippy number' because, when the last digit 9 is moved to the front, the new number produced is the slippy number multiplied by 9.

Vedic Sutra is one of many ancient Indian sutras which involves a cross subtraction method. Can you give a good explanation of WHY it works?

Countries from across the world competed in a sports tournament. Can you devise an efficient strategy to work out the order in which they finished?

This challenge is to make up YOUR OWN alphanumeric. Each letter represents a digit and where the same letter appears more than once it must represent the same digit each time.

A 3 digit number is multiplied by a 2 digit number and the calculation is written out as shown with a digit in place of each of the *'s. Complete the whole multiplication sum.

Amazing as it may seem the three fives remaining in the following `skeleton' are sufficient to reconstruct the entire long division sum.

Keep constructing triangles in the incircle of the previous triangle. What happens?

A sequence of numbers x1, x2, x3, ... starts with x1 = 2, and, if you know any term xn, you can find the next term xn+1 using the formula: xn+1 = (xn + 3/xn)/2 . Calculate the first six terms of this. . . .