# Fibonacci Numbers

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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!