Also referred to as Leonard of Pisa, Fibonacci was an Italian number theorist. It is believed that Leonardo Pisano Fibonacci was born in the 13th century, in 1170 (approximately), and that he died in 1250.

### Background

Fibonacci was born in Italy but obtained his education in North Africa. Very little is known about him or his family and there are no photographs or drawings of him. Much of the information about Fibonacci has been gathered by his autobiographical notes which he included in his books.

However, Fibonacci is considered to be one of the most talented mathematicians of the Middle Ages. Few people realize that it was Fibonacci that gave us our decimal number system (Hindu-Arabic numbering system) which replaced the Roman Numeral system. When he was studying mathematics, he used the Hindu-Arabic (0-9) symbols instead of Roman symbols which didn't have 0's and lacked place value. In fact, when using the Roman Numeral system, an abacus was usually required. There is no doubt that Fibonacci saw the superiority of using Hindu-Arabic system over the Roman Numerals. He shows how to use our current numbering system in his book Liber abaci.

The following problem was written in his book called Liber abaci:

*A certain man put a pair of rabbits in a place surrounded on all sides by a wall. How many pairs of rabbits can be produced from that pair in a year if it is supposed that every month each pair begets a new pair, which from the second month on becomes productive?*

It was this problem that led Fibonacci to the introduction of the Fibonacci Numbers and the Fibonacci Sequence which is what he remains famous for to this day. The sequence is 1, 1, 2, 3, 5, 8, 13, 21, 34, 55... This sequence shows that each number is the sum of the two preceding numbers. It is a sequence that is seen and used in many different areas of mathematics and science.

The sequence is an example of a recursive sequence. The Fibonacci Sequence defines the curvature of naturally occurring spirals, such as snail shells and even the pattern of seeds in flowering plants. The Fibonacci sequence was actually given the name by a French mathematician Edouard Lucas in the 1870s.

### Mathematical Contributions

Fibonacci is famous for his contributions to number theory.

- In his book, "Liber Abbaci," he introduced the Hindu-Arabic place-valued decimal system and the use of Arabic numerals into Europe.
- He introduced us to the bar we use in fractions, previous to this, the numerator has quotations around it.
- The square root notation is also a Fibonacci method.

It has been said that the Fibonacci numbers are Nature's numbering system and apply to the growth of living things, including cells, petals on a flower, wheat, honeycomb, pine cones, and much more.

### Books by Leonardo Pisano Fibonacci

- Liber Abbaci (The Book of Calculation), 1202 (1228)
- Practica Geometriae (The Practice of Geometry), 1220
- Liber Quadratorum (The Book of Square Numbers), 1225
- Flos (The Flower), 1225
- Letter to Master Theodore

Be sure to check out Ted, our Spreadsheet's Guide tutorial on using a spreadsheet to create the Fibonacci Numbers.