The Fibonacci Sequence is the series of numbers:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, …

The next number is found by adding up the two numbers before it:

- the 2 is found by adding the two numbers before it (1+1),
- the 3 is found by adding the two numbers before it (1+2),
- the 5 is (2+3),
- and so on!

Example: the next number in the sequence above is 21+34 = **55**

It is that simple!

Here is a longer list:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10946, 17711, 28657, 46368, 75025, 121393, 196418, 317811, …

When we make squares with those widths, we get a nice spiral:

Do you see how the squares fit neatly together?

For example 5 and 8 make 13, 8 and 13 make 21, and so on.

So we can write the rule:

The Rule is **x _{n} = x_{n−1} + x_{n−2}**

where:

**x**is term number “n”_{n}**x**is the previous term (n−1)_{n−1}**x**is the term before that (n−2)_{n−2}

This spiral is found in nature!

Plants can grow new cells in spirals, such as the pattern of seeds in this beautiful sunflower.

The spiral happens naturally because each new cell is formed after a turn.

### About Fibonacci The Man

His real name was Leonardo Pisano Bogollo, and he lived between 1170 and 1250 in Italy.

“Fibonacci” was his nickname, which roughly means “Son of Bonacci”.

As well as being famous for the Fibonacci Sequence, he helped spread Hindu-Arabic Numerals (like our present numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9) through Europe in place of Roman Numerals (I, II, III, IV, V, etc). That has saved us all a lot of trouble!