Leonardo of Pisa (Fibonacci)
Native spelling: Leonardo Pisano Bigollo
1170–1250, Pisa, Italy, Pisa, Italy
Italian merchant's son who, after learning Hindu-Arabic arithmetic in North Africa, wrote the Liber Abaci (1202) introducing the Hindu-Arabic decimal numeral system to Latin Europe, and posed the rabbit problem whose solution is the sequence now known as the Fibonacci numbers.
Leonardo, later known by the nickname Fibonacci (a 19th-century coinage from filius Bonacci, 'son of Bonaccio'), was born around 1170 in Pisa, then a powerful maritime republic in what is now Italy, the son of the merchant and customs official Guglielmo. As a boy he accompanied his father to Bugia, a Pisan trading post on the North African coast in present-day Algeria, where he was taught arithmetic by local Arabic-speaking teachers and first encountered the Hindu-Arabic decimal place-value system with its zero — a striking contrast to the cumbersome Roman numerals still used in commercial Europe.
Leonardo travelled widely around the Mediterranean, visiting Egypt, Syria, Greece, Sicily and Provence to study different mercantile and mathematical traditions, before returning to Pisa around 1200 to work as a scholar and writer. His major work, the Liber Abaci (Book of Calculation, 1202, revised 1228), is an encyclopedic manual of practical arithmetic — conversions, currency exchange, profit-sharing, and much else — that systematically taught readers the Hindu-Arabic numerals and place-value computation, doing more than any other single text to establish that system in the Latin West. Among its recreational problems is one about the growth of a rabbit population, whose solution is the sequence 0, 1, 1, 2, 3, 5, 8, 13, 21, ..., in which each term is the sum of the two preceding ones; the sequence was not named after Fibonacci until centuries later, but the problem in the Liber Abaci is its first known appearance in the Western mathematical literature.
Leonardo also wrote Practica Geometriae (1220), applying algebraic methods to practical geometric measurement and surveying, and Liber Quadratorum (The Book of Square Numbers, 1225), an advanced and original work of number theory dedicated to Emperor Frederick II, who took a personal interest in mathematical contests involving Leonardo. In 1240 the Republic of Pisa granted him a civic pension in recognition of his services advising the city on accounting matters. Documentation of his life effectively ends soon after 1241, and historians place his death around 1250, in Pisa.
Workplaces: Republic of Pisa
Italy