7
7 is a prime number.

1, 3, 4, 7, 11, 18, 29...
A Lucas number.

= 2 - 1
A Mersenne prime.

There are seven days in a week.

Hept- or Sept- means seven. A heptagon is a figure with seven sides and a heptachord is a seven-stringed musical instrument. A septennium is a period of seven years and September used to be the seventh month in the year, but not any longer.

The Seven Deadly Sins are avarice, envy, gluttony, lust, pride, sloth and wrath (listed in alphabetical order, not order of wickedness).

Among many things that come in sevens are the Seven Wonders of the Ancient World, the Seven Sisters, Shakespeare's Seven Ages of Man, the Seven Levels of Hell, and the Seven Dwarves.

Netball and water polo are both played with teams of seven players.

In Britain the 20p and 50p coins both have seven sides.

Under British law, when you reach the age of seven you can open and draw money from a National Savings Bank account or a Trustee Savings Bank account.

7-Up is a soft drink. It was invented in America in the 1920s by Mr C L Griggs of Missouri who originally called it Bib-label Lithiate Lemon-Lime Soda. With a name like that sales were poor even though the drink tasted good and so Mr Griggs set about changing the name. After six attempts he came up with 7-Up, or so the story goes. 7-Up is also the name of a card game.

John Sturges's 1960 western The Magnificent Seven is about a Mexican village that hires seven gunmen for protection from bandits. The story is based on an earlier Japanese film made in 1954 - Akira Kurosawa's The Seven Samurai.

Roy Sullivan, a park ranger from Virginia, USA is the only person to have been struck by lightning seven times. Between 1942 and 1977 he was struck on top of his head (twice), his eyebrows, his shoulder, his chest, his ankle and his big toe. Although he received hospital treatment for his injuries, he was extraordinarily lucky to escape death from so many strikes.


8
= 2 x 2 x 2A cube.
= 2 x 4
1, 1, 2, 3, 5, 8, 13... A Fibonacci number.
Eight pints make a gallon.
Eight is the third number that stays the same when written upside down.
There are eight legs on a spider, barring accidents. Scorpions also have eight legs.
An eight is a racing boat with eight oars. Its crew is also called an eight. There are eight people in a tug-of-war team.
Some large car engines have eight cylinders.
According to Indian mythology, the Earth is supported on the backs of eight white elephants.
Before the rise of Christianity, there were eight days in the Greek and Roman weeks.


Eight-fold symmetry is common in decoration.
Pieces of eight go with pirates and parrots. Originally they were piastre - Spanish silver coins of the seventeenth and eighteenth centuries marked with an `8' because they were worth eight reals. The dollar sign $ is probably derived from the figure `8' as it appeared on `pieces of eight'.
In the game of pool the Eight Ball is a black ball with the number 8. The expression `behind the eight ball' means to be in a difficult or baffling situation.
A cube has eight corners or vertices.
Many words beginning oct- are related to the number eight. An octopus has eight arms and an octet is a group of eight musicians. (An octet of octopuses would therefore have 64 arms between them.)
An octagon is a figure with eight sides and an octahedron has eight faces.


9
= 3 x 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.

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.

10
= 2 x 5
= 1 + 2 + 3 + 4 A triangular number.
= 1 + 3 + 6A tetrahedral number - the sum of the first three triangular numbers.
If a number ends with a zero it is exactly divisible by ten.
We have ten digits on our hands, and ten is the base of our number system: the decimal system. The Roman symbol for ten is X, perhaps representing two crossed hands.
The ten pins in a bowling alley are arranged in a triangular pattern.
Virgins, according to the Bible, come in tens: five foolish and five wise.
A dime is a ten cent piece in the USA.
Deca- means ten. So a decade is ten years, a decagon has ten sides and a crab is a decapod because it has ten feet. The Decalogue is a name for the biblical Ten Commandments.
A tithe means a tenth. It was the levy imposed by the church of one tenth of the produce of land and stock.
Men's lacrosse is played with teams of ten players.
Metric measurements use units in multiples of ten. In this context deca- means ten times so ten metres equals one decametre. Deca- is sometimes abbreviated to da. Deci- means one tenth so ten decimetres make a metre and ten decilitres make a litre. Deci- is sometimes abbreviated to d.

11
11 is a prime number.
1, 3, 4, 7, 11, 18, 29... A Lucas number.
The Eleven Plus was an English school selection examination taken by 11 year olds which was abolished in most areas with the introduction of comprehensive schools. It is still fondly remembered by taxi drivers and education ministers.
Elevenses is a mid-morning refreshment such as tea and biscuits taken around 11am.
Soccer, cricket, American football and field hockey are all played with teams of 11 players on the field.
The sun spot cycle repeats about every 11 years. Sun spots are dark spots on the surface of the sun. They occur more often during the active phase of the sun spot cycle. The spots have intense magnetic fields which are associated with magnetic storms on earth. Radio reception on earth is also affected by the sun spot cycle.

12
= 2 x 2 x 3
= 2 x 6= 3 x 4
= 2 + 4 + 6= 3 + 4 + 5
A dozen.
There are 12 months in a year,
12 inches in a foot and 12 old pennies in a shilling.
12 o'clock is midday or midnight. There are 12 signs of the Zodiac,
12 apostles and 12 people in a jury.

A dodecahedron has a regular pentagon on each of its 12 faces. It is one of the five Platonic solids. It has 20 vertices (or corners) and 30 edges. If you join together the centres of the faces of a dodecahedron you get an icosahedron.
Both octahedrons and cubes have 12 edges. An icosahedron has 12 vertices or corners.
The wheels of most cars are held on by 16 wheel nuts, with four for each wheel. Two important exceptions to this rule are the Citroën 2CV and the Robin Reliant which each have just 12 wheel nuts. The Citroën 2CV has three wheel nuts on each of its four wheels, while the Robin Reliant has four wheel nuts on each of its three wheels.

13
13 is a prime number.
1, 1, 2, 3, 5, 8, 13...A Fibonacci number.
A baker's, devil's or long dozen.
13 is the `unlucky number' and Friday the 13th is supposed to be particularly unlucky.
If April 13 is a Friday, how many days will it be to the next Friday the 13th? What is the shortest possible interval between two Friday the 13ths? What is the longest possible interval?
Triskaidekaphobia is the fear of the number 13, for example, of 13 people sitting at a table.
'Eleven plus two' is an anagram of 'twelve plus one'.
Thirteen is the number of hearts in a pack of cards.
Rugby League is played with teams of 13 players.
Under British law, when you reach the age of 13 you can get a part-time job, but you cannot work for more than two hours on a school day or a Sunday.

14
= 2 x 7
= 1 + 4 + 9 A pyramidal number - the sum of the first three square numbers.
= 2 + 3 + 4 + 5

A pyramid of 14 balls.
There are 14 pounds in a stone and 14 days in a fortnight.
February 14 is St Valentine's day.
The humble woodlouse has 14 legs arranged as seven pairs.
The flag of Myanmar (formerly Burma) has 14 stars representing its 14 states.
The French word for a fortnight is quinze jours or 15 days. If a fortnight begins and ends on a Tuesday, does it contain two Tuesdays or three Tuesdays? And so does it have 14 days or 15 days? Who is being more logical? The French or the English?

15
= 3 x 5
= 1 + 2 + 3 + 4 + 5 A triangular number.
Rugby Union is played with teams of 15 players.
15 is the constant of a 3 x 3 magic square.
Under British law, when you reach the age of 15 -
if you are a boy, under certain circumstances you can be sent to prison to await trial,
you can see a category 15 film,
you can open a Post Office Girobank account but you must have an adult guarantor.
`15' on a bottle of sun lotion is its sun protection factor. Sunscreen products have factors like 4, 8, 15 and 20. The higher the number, the more protection from the sun you get.
The number gives you a rough idea of how long you can lie in the sun without burning -`Safe time' with sunscreen = `Safe time' without sunscreen x Sun protection factor
For example, if you have fair skin, you may be able to lie without burning for 20 minutes in the hottest midday sun in the UK (try hard to remember this if you can). But if you wear a sun lotion marked `15' the safe time is roughly 15 times greater -15 x 20 minutes = 300 minutes- or five hours. Of course you have to be careful to make sure the sunscreen does not rub off during this time.
The factor number measures how well the sunscreen blocks out the ultraviolet B (UVB) rays of the sun. These rays tan the skin but they also cause burning and are a major cause of skin cancer.

16
= 2 x 2 x 2 x 2 A fourth power.
= 4 x 4A square.
= 2 x 8
= 1 + 3 + 5 + 7
There are 16 ounces in a pound.
Sixteenmo is the size of a book made by folding each sheet of paper into 16 leaves.
In biology, if a cell divides itself in half every 30 minutes, you will have 16 cells in 2 hours.
16 pieces are used by each player in a game of chess.
Caterpillars typically have 16 legs. But when they emerge from their chrysalis as a butterfly or moth, they have only six legs.
Under British law, when you reach the age of 16 -
you can leave school,
you can marry with parental consent (or without it in Scotland),
if you are convicted of an imprisonable offence, you can be given a community service order,
if you are a boy, you can join the armed forces with parental consent,
you can drive an invalid carriage or a moped,
you can buy cigarettes and tobacco,
you can have beer, cider or wine with a meal in a restaurant,
you may become a street trader.

17
17 is a prime number.
In 1963 the Italian film director Federico Fellini released an autobiographical film Eight and a Half. A few years later a film called Seventeen was released and one film critic, who could not resist making a comparison, headed his newspaper review 'Seventeen - twice as good as Eight and a Half".
Under British law, when you reach the age of 17 -
criminal charges against you will be dealt with in the adult courts,
you can hold a licence to drive most vehicles,
you can buy or hire any firearm or ammunition.

18
= 2 x 3 x 3
= 2 x 9= 3 x 6
= 3 + 4 + 5 + 6
1, 3, 4, 7, 11, 18, 29... A Lucas number.
Australian rules football is played with teams of 18 players.
There are 18 holes on many golf courses.
18deg. Celsius is usually considered a comfortable room temperature.
The two 18 letter words `conservationalists' and `conversationalists' are anagrams of each other. They are the longest pair of anagrams in the English language if scientific words are excluded.
Eighteenmo is the size of a piece of paper which has been made by cutting a larger sheet of paper into 18 equal pieces. It is also the name for a size of book that has been made in the same way.
In the UK, the names of race horses can be no longer than 18 characters, including spaces.