**Leonardo Pisano**, was born in 1170, and died after 1240. Also known as Leonardo de Pisa or **Leonardo Fibonacci**, was the first great mathematician of medieval Christian Europe. He played an important role in reviving ancient mathematics and making significant contributions.

Liber Abacci (Book of Abacus, 1202), his treatise on arithmetic and elementary algebra, introduced the modern Hindu-Arabic system of numbers using ten symbols. His most important original work is on indeterminate analysis and number theory. The FIBONACCI SEQUENCE is named by him. *Mis practice geometry* (Geometry Practice, 1220) gave a compilation of time geometry and also introduced some trigonometry.

## The Fibonacci Sequence

A Fibonacci sequence is a sequence in which each term is the sum of the two terms preceding them. It was named that way because Fibonacci was the discoverer. The succession of Fibonacci, which has 1 as its first term is:

1, 1, 2, 3, 5, 8, 13, 21, 34, 55,…

Numbers can also be called *Fibonacci numbers*. This equation is a recursion relation, or recurrence relation that relates different terms of a sequence or series. Fibonacci sequences have proven useful in number theory, geometry, continuous fraction theory, and genetics. They also arise in many seemingly unconnected phenomena, for example, the GOLDEN SECTION, a form valued in art and architecture because of its pleasing proportions, and the spiral arrangement of petals and branches in certain types of flowers and trees.

Bibliography: Gies, Joseph and Frances, Leonardo of Pisa and the New Mathematics of the Middle Ages (1969).

Garland, T.H., Fascinating Fibonaccis (1987); Hoggatt, V. E., Fibonacci and Lucas Numbers (1969); Vorobev, N.N., Fibonacci Numbers (1961; repr. 1983.