I’m a bit of a numbers fan.

I often count the sum of steps on stairs and I’m chuffed when it’s a prime number.

Nerd? Maybe.


I love playing with numbers and take delight when they do clever stuff.

Geek? Probably.

And I especially love 17.


Here are 17 reasons why 17 is a cool number

1) 17 is a prime number (only divisible by 1 and itself) ☝️

2) 17 is the sum of the first four prime numbers: 2 + 3 + 5 + 7 🤓

3) Haiku, a form of Japanese poetry, traditionally has 17 syllables 🇯🇵

4) In the UK you can start to drive at 17 – beep beep! 🚙

5) There are 17 keys in the key of a standard piano octave 🎹

6) In geometry, a 17-sided polygon is known as a HEPtadecagon – love the HEP 😌

7) Apollo 17 was the last manned mission to the moon 🌖

8) The Leaning Tower of Pisa has 17 floors 🍕

9) There are 17 known moons of Uranus 🌕

10) According to Greek mythology, the rainbow has 17 colours 🌈

11) The record for the most people crammed into a Smart car is 17 🚘

12) 17 is a significant number in blackjack 🃏

13) In numerology, 17 is seen as a combination of 1 and 7, symbolising new beginnings (1) and good fortune (7) 🥠

14) March 17 is St Patrick’s Day ☘️

15) In Roman numerals, 17 is written as XVII – it was considered a symbol of immortality 💪🏼

16) The fastest red card in professional football was issued 17 seconds after kick-off 🟥

17) The Michael Heppell Black Friday Sale is based entirely on 17 – tenuous link, I know. You can grab amazing offers on the book, the audio, DAY17 and my private coaching group TEAM17.

Last week I asked you to vote on whether we should have a sale. You decided 6:1 that we SHOULD!

And in true Black Friday tradition, the offers are amazing.

Take a look and please leave your Why 17 is a cool number comments below.

Be Brilliant!



  1. November 23rd 2023 by David Viner

    There are definitely NOT 17 keys in an octave – from middle C to the C above is a distance of 12, not 17! I know 12 looks a bit like 17 from a distance – should’ve gone to Specsavers! 😉

  2. November 23rd 2023 by Judith (Judy) Brulo

    There are 13 keys in an octave.

  3. November 23rd 2023 by Dave Barker

    There are exactly 17 wallpaper symmetry patterns

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