*Photo by *vlad* licensed CC BY-NC 2.0*

November 23 is very special day if you love math, but do you know why? Well, November 23 can be written like this: 11/23. Why is that so special? That’s the start of what is called the* Fibonacci sequence (say ‘fib-oh-NAH-tchee’)* — a mathematical set of numbers that can be found everywhere! It all started with a guy named Leonardo (but not the Ninja Turtle)...

Leonardo Bigollo, better known as Leonardo Fibonacci, was an Italian mathematician who lived over 900 years ago in the 1200s. Fibonacci’s the guy that gave us the *decimal number system* (that’s another way to say the numbers we use right now: 1, 2, 3, 4, 5, 6, 7, 8, 9 and 0). Prior to him, lots of people used *Roman numerals* (I, II, III, IV, V, VI, VII, VIII, IX and so on). But that’s not even what he’s most famous for!

*A pair of bunnies helped Fibonacci discover the answer to a big math problem.*

Leonardo had a math problem he wanted to figure out: If one pair of bunnies gives birth to another pair of bunnies two months after their birth, and then those bunnies give birth to another two bunnies two months later, and so on and so on, how many bunnies would you have after one year? It’s kind of a silly question, but it led to a very important discovery — a series of numbers that look like this:

What makes them special is that each number in the sequence is found by adding the two numbers in front of it. So, the first two numbers are 1 + 1, which equals the third number, 2. And then the next two numbers are 1 + 2, which equals the fourth number, 3. And then if you take the 2 and add it to the 3, you get the next number, 5…

*Yeah, what about those bunnies?*

So if you have a pair of bunnies that gives birth to another pair of bunnies, and then 2 months later, that pair has another pair (and so on), the answer is:

And that's called the Fibonacci sequence (it's named after Leonardo!).

*You can even find the sequence when you examine a pine cone. (Photo credit: adam hilliker via Visual hunt / CC BY-NC-ND)*

It was discovered that these numbers appear in many ways in nature. The bunny question was just a theory, but when scientists looked at examples in nature — from animals to plants — they found the number sequence everywhere!

*The Fibonacci spiral kind of looks like a seashell.*

And when you draw the number out on paper using larger and larger squares to show each number, they create a spiral, like the kind you’d see in a sea shell or a the centre of a flower.

Actually, scientists have discovered that when you count the spirals in the centre of a sunflower, the numbers almost always match those of the Fibonacci sequence!

*Look at a spiral staircase from below and you will see the Fibonacci spiral. (Photo credit: cleber via VisualHunt.com / CC BY-NC)*

The same goes for flower petals, acorns, spiral staircases, scales of a pineapple and the inside of a shell. Even the inside of a banana has ties to the Fibonacci sequence.

*Even Sonic the Hedgehog was designed with math! (Photo credit: doublecompile via VisualHunt.com / CC BY-SA)*

Even artists, musicians, architects and others have been using the Fibonacci sequence and the spiral that it creates (even if they don't think they're using math!) for ages to make their creations more beautiful. Wild!

Once you know how to look for it, you will see the sequence everywhere. Cool, right? See if you can find the Fibonacci spiral in everyday objects around you.