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A Short and Sweet Guide to the Number Seven

 

Ask someone what their favourite number is, and there’s a good chance they’ll answer seven.

In an online survey of about 44,000 people, nearly 10% picked seven. Alex Bellos, the mathematician who ran the study, hypothesises that its popularity is down to it being “arithmetically unique”.

 

What does this mean? Seven is the only number below ten that you cannot be multiplied or divided and still be a whole number under 10:

  • The numbers 1, 2, 3, 4 and 5 can be doubled and always between 1 - 10
  • 6, 8 and 10 can all be halved
  • 9 divides by 3

 

Seven is left all by itself; it’s unique. Bellos speculates that it’s this very uniqueness that makes it so appealing to so many people. 

 

Number 7 in the World Today

The number seven shows up a lot in human culture. Here are just some of the places we see 7 in everyday life:

 

  • Number of days in the week
  • Continents in the world
  • Seven basic musical notes, namely, 'do', 're', 'me', 'fa', 'so', 'la' and 'te'. 
  • Seven dwarves with Snow White

7 is also the most likely number to come up when adding the total of two dice rolls

 

7 in the Ancient World

But the number seven goes back further. For example, there are seven wonders of the ancient world: 

  • The Great Pyramid of Giza
  • The Hanging Gardens of Babylon
  • The Temple of Artemis at Ephesus
  • The Statue of Zeus at Olympia
  • The Mausoleum at Halicarnassus
  • The Colossus of Rhodes 
  • The Lighthouse of Alexandria.

 

There were also seven sages in Ancient Greece, seven liberal arts established in Roman education, seven digits in the Roman numerical system (I, V, X, L, C, M, D), as well as the seven hills in Rome itself.  At the time, it was also believed that there were seven celestial bodies in the night sky: the Sun, the Moon, Venus, Mercury, Mars, Jupiter and Saturn.



Making patterns fit number 7

We’re all familiar with the seven colours of the rainbow. However, did you know that in Medieval times, people commonly believed the rainbow was made of just five colours: red, yellow, green, blue and violet. 

 

When Issac Newton split light through a prism, he added orange and indigo to make it seven in total. He did this because he believed, in common with the Ancient Greeks and Romans, that there was a connection between the number 7 and the number of days in the week, the number of notes in a musical scale and the number of objects then known in the solar system.

 

Seventh Month in the Calendar

July is the seventh month of our calendar. But this wasn’t always the case. In the Roman calendar, it was September - the name for the month comes from the Roman word ‘septem’.

 

Today, we use the Gregorian calendar, which is named after Pope Gregory XIII. He first introduced the calendar in 1582. In Britain, we used the Julian calendar until 1753. It was based on the solar year. It was 365.25 days, which meant that over time the calendar became out of sync with the seasons. 

 

In 1752, Britain decided to adopt the Gregorian calendar. But doing this meant that 3rd September 1752 became 14th September 1752. So, technically, in British history, nothing whatsoever happened between 3rd and 13th September because these days never existed. 

 

What’s your favourite number? There’s a good chance, based on the odds, that it’s 7!

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