Number 9


= 3 × 3
A square.

= 1 + 3 + 5
= 2 + 3 + 4

There are nine major planets in the solar system, Beethoven wrote nine symphonies, and a cat is said to have nine lives.

A polygon with nine angles and nine sides is called a nonagon.

In French the word neuf means both nine and new. In German, the words for nine and new are neun and neu, and in Spanish, nueve and nuevo. As you count and reach nine, you know you are about to make a new start.

Spinning top game
In this Black Forest game, a spinning top throws coloured balls into nine holes arranged as a nonagon.

Rounders and baseball are all played with teams of nine players.

A game of squash is won by scoring nine points.

Golf courses often have nine holes.

The expression to the nines means to the highest degree.

The game of skittles or ninepin bowling is many hundreds of years old. The pins are set up in a diamond formation and players throw the ball (or 'cheese') at them. In the nineteenth century some American states passed laws banning the game because bets were often placed on it. But these laws were evaded by the simple ruse of adding a tenth pin. As a result tenpin bowling is now the far more popular game.

Over the years, the number of pins used for bowling has varied from as few as three to as many as 17. Can you invent a good way to set up the pins for any number between three and 17?

Number 9

Swedish stamp displaying an 'impossible figure'
The nine cubes on this Swedish stamp make an 'impossible figure'. This arrangement cannot exist in the real world.

On cloud nine means happy, euphoric or 'high'. The phrase came into use in the 1950s from a term used by the US Weather Bureau. For the meteorologists Cloud Nine is cumulo-nimbus cloud at a height of 10 km, which is high even by the standard of clouds.

Only about one ninth of the mass of an iceberg is visible above the water. Nearly all its bulk remains hidden beneath the surface.

In the film 2001 the famous black monolith was a cuboid with sides in the ratio 1 : 4 : 9. These are the first three square numbers.

The 9 of diamonds - the playing card - is sometimes called the Curse of Scotland.

Redivider with nine letters is the longest palindromic word in the English language. A palindromic word has the same sequence of letters backwards or forwards.

The game of Shove Ha'penny uses a board divided into nine 'beds' or rows. The winner is the first player to place 3 coins into each bed.

A nine days' wonder is something that creates a short-lived sensation.

It is easy to work out whether a number is exactly divisible by 9. This is the same as asking whether a number is in the '9 times table'. All you have to do is add up its digits. If the answer is more than one digit long, you add up the digits again, and go on doing this, until you are left with a single digit. If this single digit is 9 then the original number was divisible by 9.

For example, is 781236 divisible by 9? Adding up its digits –
7 + 8 + 1 + 2 + 3 + 6 = 27
– and adding again –
2 + 7 = 9
– and because the answer is 9, the original number must be divisible by 9.

You can also use this method to find out if a number is divisible by 3. If the single digit is a 3, 6 or 9, then the original number was divisible by 3.

Here is a game for two players which uses nine coins.

Arrange the coins in a circle. The players take turns and can remove either one coin or two coins which are next to each other. The winner is the player who picks up the last coin.