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# Number 7: Is seven the lucky number?

Think of a number between 1 and 10. How many colours in a rainbow? (Hint: strictly more than 7!) What is cyclic permutation? And an awe-inspiring champion boxer.

This week being NAIDOC Week, I took my mum to the incredible SandSong performance by Bangarra Dance Theatre. A powerful exploration of the world's longest continuous culture from the Dreamtime through to modern-day Australia. Bangarra is a national treasure and I can't recommend SandSong trongly enough.

## Seven - the lucky number?​

The great English puzzle master and mathematics populiser Alex Bellos once surveyed 30,025 people about their favourite number. Their answers were perhaps surprising, with 1,123 different digits nominated. Every number from 1 to 100 was selected by at least one person as their fave. Numbers 2 through 9 all featured in the top 10, whereas 1 and 10 were merely the 21st and 23rd most popular numbers – even π finished in front of them! 110 was the lowest number to receive zero votes, leading Alex to call it ‘surely the world’s least-loved number’. And the most loved number on the list? Alex’s survey confirmed what many others have also found. When you ask a person for their favourite number, or ask someone to pick a number from 1 to 10, they are most likely to choose 7. It’s why I’ve often considered 7 the most overrated of all the numbers! What’s your favourite number, and why? Hit me up at number@adamspencer.com.au and I’ll include some responses in my next newsletter.

## Enjoy these fascinating numerical facts about 7!

Roy G. Biv​ At primary school we are taught there are 7 bands of colour in a rainbow - red, orange, yellow, green, blue, indigo and violet*. ​ These are often committed to memory through a mnemonic like ‘Richard of York Gave Battle In Vain’ or the fictional character Mr Roy G. Biv.

Licence to kill​ The fictional MI6 agent James Bond goes by the number 007, with the 00 prefix signifying he has an elite 'licence to kill' and can shoot with no questions asked. The 7th Bond film is Diamonds Are Forever starring Sean Connery who has played this iconic spy seven times!

Lightning strike American park ranger Roy Cleveland Sullivan survived 7 lightning strikes between 1942 and 1977. Taking the sometimes quoted odds of being struck by lightning as 1:10000, the probability of being hit seven times is (1:10000)7 = 1:1028, or 1 in 10,000,000,000,000, 000,000,000,000,000.

* Actually you can argue that a rainbow contains lots more than 7 colours. Along the visible light spectrum from red (the longest wavelength at around 780 nm) through to violet (the shortest wavelength in the sequence at 380 nm), there are theoretically a million different colours that most human eyes could detect. That would make for quite a long mnemonic, so let’s stick to 7!

## INSPIRATIONAL THINKERS & DOERS - Lovemore Ndou, From jail to boxing champ and lawyer with seven degrees

It was a thrill to MC the recent Steadfast Group Limited Convention in Adelaide and to finally bring on the clash everyone has been waiting for – The Spence vs 3-time world light-welterweight champion Lovemore Ndou. ​ Lovemore’s life story is chilling and inspirational. Suffice to say, the scar over his right eye is not from the boxing ring in Las Vegas, but a police interrogation cell in his native South Africa. He spoke passionately about his troubled childhood, his failed football career (he got into fights when people tried to take the ball off him!) and the brutal discipline that boxing demands of its practitioners. ​ Motivated by injustice in his homeland, Lovemore who is one of 7 children has since accumulated 7 university degrees in fields as diverse as human rights law, criminal prosecution and communications. He is now flourishing as a lawyer with his own legal practice and does pro bono work for those less fortunate. Oh, and he’s also conversant in 7 African languages plus fluent in English and Afrikaans. ​ His book Tough Love tells his story. So if you're organising an event and you want an uplifting tale, Lovemore Ndou is the man for you. ​ And in case you're wondering, he dropped me in the 7th!

## Seven and the case of cyclic permutation

The number 142,857 has a wonderful property deeply connected to the number 7. ​ Multiply it by 2 and you get 285,714 which contains the digits of 142,857 in the same order except with the ‘14’ moved to the back. We call this a ‘cyclic permutation’ – 'permutation' means rearrangement and ‘cyclic’ means the order of the numbers is maintained. ​ That’s pretty cool, but it gets more awesome! Continue to multiply 142,857 by each of the numbers 3 through 6 and you get: ​ 142857 × 3 = 428571 142857 × 4 = 571428 142857 × 5 = 714285 142857 × 6 = 857142 Of course you now want to multiply it by 7 - well go ahead! You will get 142857 × 7 = 999999, which actually is the reason why the cyclic permutation occurs. It is also why if you write 1/7 as a decimal you will get 0.142857 142857 142857 142857 142857 … with the numbers 142857 repeating forever. ​ Okay, so maybe 7 is not overrated after all!

## Two more reasons why 7 is perhaps not overrated

Firstly, 7 is involved, indirectly, in this gorgeous little equation: (3 + 4)3 = 343 ​ Secondly, there are 7 notes in the chromatic musical scale - A, B, C, D, E, F and G. Some wordsmiths refer to words composed of only these letters as ‘piano words’; for example, cage, bag and edge. What is the longest piano word you can think of? Hit me up at number@adamspencer.com.au and I'll give away some books to my fave answers. ​ Yours in numbers, Adam