Happy Fibonacci Day!

Leonardo Pisano Bigollo (1170-1250), known today as Fibonacci, was one of the most talented mathematicians of the Middle Ages. He was instrumental in introducing the Hindu-Arabic number system to Europe through his book, Liber Abaci or the Book of Calculations. One example in this book is the sequence that today bears his name and begins 1, 1, 2, 3, 5, 8, 13, 21 ... in which each term is the sum of its two predecessors. Thus 5/8/13 has been dubbed "Fibonacci Day."

The Fibonacci Sequence and the Fibonacci Spiral appear throughout nature.

The Fibonacci Sequence was first used to model rabbit populations.

The Fibonacci Sequence is often seen in flowers and other plants. This daisy has two rows of petals; eight in front and thirteen behind.

The Fibonacci Spiral also describes many forms found in nature, such as this nautilus shell.

Hurricane Irene in the form of a Fibonacci Spiral.