23 Fascinating Maths Facts You'll Probably Never Need To Use

Proof is left as an exercise for the reader.

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3. The spiral shapes of sunflowers follow a Fibonacci sequence.


That's where you add the two preceding numbers in the sequence to give you the next one. So it starts 1, 1, 2, 3, 5, 8, 13, 21, etc. The Fibonacci sequence shows up in nature a fair bit.

4. The Fibonacci sequence is encoded in the number 1/89.

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1/89 = 0.01 + 0.001 + 0.0002 + 0.00003 + 0.000005 + 0.0000008 + 0.00000013 + 0.000000021 + 0.0000000034 etc.

5. A pizza that has radius "z" and height "a" has volume Pi × z × z × a.


Because the area of a circle is Pi multiplied by the radius squared (which can be written out as Pi × z × z). Then you multiply by the height to get the total volume.

8. In a room of just 23 people there’s a 50% chance that two people have the same birthday.


It's called the Birthday Problem. In a room of 75 there's a 99% chance of two people matching.

11. We tend to think of odd numbers as male and even numbers as female.


This ancient belief was tested by James Wilkie and Galen Bodenhausen of Northwestern University. In his latest book, Alex Bellos writes: "They showed respondents randomly assigned pictures of the faces of young babies, each next to a three-digit number that was either odd-odd-odd or even-even-even, and asked them to guess the baby’s sex [...] Respondents were about 10 per cent more likely to say that a baby paired with odd numbers was a boy, than if the same baby was paired with even numbers."

16. That might be because 7 is "arithmetically unique".

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It's the only number below 10 you can't multiply or divide and keep within group. For example, 5 you can multiply by 2 to get 10 (still within the 1-10 group), 6 and 8 you can divide by 2.

17. 7 also shows up a lot in human culture.


We have seven deadly sins, and seven wonders of the world. Not to mention colours of the rainbow, pillars of wisdom, seas, dwarves, days in the week...

This might be because when these things came about there were celestial bodies visible in the sky (the Sun, the Moon, Venus, Mercury, Mars, Jupiter and Saturn).

18. The number 4 is considered unlucky in much of Asia.

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That's because the words for "four" in Japanese, Cantonese, Mandarin and Korean (shi, sei, si, sa) sound the same as the words in those languages for death.

19. .999999... = 1

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Here's the proof:

If 10N = 9.9999...

Then N = .9999....

Subtract N from 10N, leaving you with 9N=9.

So then N=1. But we already know that N=.9999... as well.

So 1=.9999....

20. Cicadas use prime numbers as an evolutionary strategy.

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Cicadas incubate underground for long periods of time – 13 or 17 years – before coming out to mate. 13 and 17 are both prime numbers. It's thought cicadas ended up in these prime number life-cycles because it meant they came into contact with predators on more round numbered life-cycles less often.

21. 10! seconds is exactly 6 weeks.


10! means 10 factorial. 10! = 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1 = 3628800 seconds. Which is 42 days, or 6 weeks, exactly.

22. Take any four digit number, follow these steps, and you'll end up with 6174.

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1. Choose a four digit number (the only condition is that it has at least two different digits).

2. Arrange the digits of the four digit number in descending then ascending order.

3. Subtract the smaller number from the bigger one.

4. Repeat.

Eventually you'll end up at 6174, which is known as Kaprekar's constant. If you then repeat the process you'll just keep getting 6174 over and over again.

Thanks to this Reddit thread, this Quora post and Alex Bellos' new book, Alex Through The Looking Glass for some of these facts.