# Leonardo Pisano Bigollo

**Episode #5 of the c****ourse “Greatest Mathematicians”**

“The most talented Western mathematician of the Middle Ages” is also a man of many names. Leonardo Pisano Bigollo is also known as Leonardo of Pisa, Leonardo Bonacci, or by the name most people will recognize: Fibonacci. He introduced the Hindu–Arabic numeral system to Europe as well as the sequence of Fibonacci numbers, which were discovered earlier in India.

He learned of these numbers during his travels with his father, Guglielmo Bonacci, a wealthy Italian merchant who oversaw a trading post in Bugia, a port in North Africa. Born around 1170, Fibonacci traveled throughout the Mediterranean to study under the leading Arab mathematicians of the time. When he returned from his travels, he published what he had learned in *Liber Abaci*. He died sometime between 1240 and 1250, most likely in Pisa.

The Fibonacci numbers, which appear in his book, *Liber Abaci*, are some of the simplest yet farthest-reaching mathematics in the world. You may have seen this sequence of numbers: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, etc. in which each number is the sum of the previous two. This is simple addition, but these numbers also appear surprisingly often in nature. They are a natural phenomenon, proof that math is an innate part of our universe. The number of petals on a flower, for example, is usually a Fibonacci number, or the number of spirals on a sunflower or pineapple. In addition to the Fibonacci numbers showing themselves in the natural world, they also have practical importance in commercial bookkeeping, conversion of weights and measures, the calculation of interest, and money-changing, among other applications.

Perhaps Fibonacci’s most lasting and perplexing discovery was the Golden Ratio, or 1.618033. This number has fascinated mathematicians, scientists, and artists for centuries. It is the basis of the iconic spiral image associated with Fibonacci’s work.

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