# Fibonacci Numbers

There’s a special string of numbers called the Fibonacci sequence. It’s named after a fellow whose name was… can you guess it?… actually, Leonardo of Pisa, but his nickname was Fibonacci. He actually wasn’t the first person to discover this sequence – it had been known in India for centuries – but he introduced it to the Western world in his book, *Liber Abaci*, and that’s why it was named after him. (Apart from making the Fibonacci sequence famous, Leonardo helped popularize the Arabic numeral system – our counting numbers 0, 1, 2, 3, 4, etc. – which made calculations a lot easier than with the old Roman numeral system. Thank you, Fibonacci!)

So – the sequence. It starts literally as easy as $1+1=2$. From there we get the next number in the sequence by adding the two numbers before it. Here we go:

$1+1=2$ $1+2=3$ $2+3=5$ $3+5=8$ $5+8=13$ $8+13=21$

And if we keep going with this forever, we get:

$$ 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, \ldots $$

This is the Fibonacci sequence.

Okay, that’s a neat idea. Where do we go from here? Have fun exploring the marvelous Fibonacci features below!