Fibonacci's real legacy was teaching Europe to count with Arabic numerals
The rabbit sequence made his name famous, but Fibonacci's bigger gift was practical. His 1202 Book of Calculation showed European merchants how Hindu-Arabic digits, with zero and place value, beat Roman numerals for bookkeeping and interest. And the sequence itself had been described by Indian mathematicians centuries earlier.
Leonardo of Pisa was born around 1170. His father, Guglielmo, was a merchant and customs official who directed a trading post at Bugia, today Béjaïa in Algeria, and took the boy along. There Leonardo learned the Hindu-Arabic numerals. Travelling the Mediterranean, he met merchants and studied their ways of doing arithmetic, and he became convinced of the advantages of a place-value system for easy calculation.
Liber Abaci, finished in 1202, introduced what it called the method of the Indians: ten digits including zero, written positionally. It then applied them to real commerce, from converting currencies and weights to calculating interest. The original manuscript is lost; a copy from 1228 survives. The book was well received across educated Europe and made business arithmetic quicker than Roman numerals, the abacus or the old Egyptian way of multiplying.
One exercise asked how an idealised rabbit population grows. The answer, generation by generation, is the sequence in which each number is the sum of the two before. Fibonacci started at 1, 2, 3 rather than today's 0 and 1, and carried it to 233, with another manuscript reaching 377. His is the earliest known description outside India, where mathematicians had discussed the sequence as early as the sixth century.
He won royal attention as a guest of Emperor Frederick II, whose courtier John of Palermo set him problems drawn from Arab mathematics, and in 1240 Pisa granted him a salary for advising the city on accounting and teaching citizens. He died sometime between 1240 and 1250. The nickname Fibonacci, short for son of Bonacci, appears in a notary's record of 1506 and was popularised by Guglielmo Libri in 1838. A 19th-century statue of him now stands in the Camposanto in Pisa, and an asteroid bears his name.
Source: Fibonacci
