Fibonacci’s “Liber Abaci”

Leonardo was the son of a Pisan merchant and customs official who ran the trading post of Pisan merchants at Bugia (Béjaïa) in North Africa. There the boy learned the “Indian” method of reckoning; later he travelled around the Mediterranean — he names Egypt, Syria, Greece, Sicily and Provence — comparing the methods of merchants. After returning to Pisa he completed his book in 1202. It opens with the nine Indian figures and the sign 0, “which the Arabs call zephir”, with which any number can be written; its fifteen chapters go on to the operations of arithmetic, conversion of currencies, profit and interest, and recreational problems, among them the problem of breeding rabbits whose answer is the sequence later named after the author.

The 1202 text has not survived: the book is known in a revised version of 1228 dedicated to Michael Scot. Leonardo was a guest of Emperor Frederick II, whose court scholar John of Palermo set him problems, and in 1240 the Republic of Pisa granted him a salary. The new numerals spread slowly — the “algorists” and the reckoners on the abacus with Roman numerals contended for centuries, and written calculation came into general use only in the 16th century. The name Fibonacci, short for filius Bonacci (“son of Bonacci”), was popularized by a book of 1838, though a notary’s record of 1506 already calls him “Lionardo Fibonacci”.