Fibonacci, Leonardo (c. 1170–c. 1250)

Italian mathematician. He published Liber abaci/The Book of the Calculator in Pisa in 1202, which was instrumental in the introduction of Arabic notation into Europe. From 1960, interest increased in Fibonacci numbers, in their simplest form a sequence in which each number is the sum of its two predecessors (1, 1, 2, 3, 5, 8, 13, ...). They have unusual characteristics with possible applications in botany, psychology, and astronomy (for example, a more exact correspondence than is given by Bode's law to the distances between the planets and the Sun).

In 1220, Fibonacci published Practica geometriae, in which he used algebraic methods to solve many arithmetical and geometrical problems.

Fibonacci was born in Pisa. He learned mathematics in Algeria and travelled extensively in the Mediterranean region. Returning to Pisa in about 1200, he began his mathematical writings. In 1225 he won a mathematical competition in Pisa in the presence of Holy Roman Emperor Frederick II. A marble tablet dated 1240 is thought to refer to Fibonacci as being awarded an annual pension for his accountancy services to the state.

Liber abaci was a thorough treatise on algebraic methods and problems in which he strongly advocated the introduction of the Indo-Arabic numeral system, comprising the figures 1 to 9, and the innovation of the ‘zephirum’ – the figure 0 (zero). Dealing with operations in whole numbers systematically, he also proposed the idea of a bar (solidus) for fractions.