The numbers 3, 5, 8, 13, and 21 are all Fibonacci numbers—members of a sequence in which successive numbers are sums of the preceding two numbers, starting with 1 and 1: 1, 1, 2, 3, 5, 8, 13, 21 ...

To carry out their calculations, merchants in the early 13th century used an abacus or a system called finger reckoning. Commerce changed when Leonardo of Pisa — known today as Fibonacci ...

In 1202 Leonardo da Pisa (aka Fibonacci) taught Western Europe how to do arithmetic with Arabic numerals. In Man of Numbers: Fibonacci's Arithmetic Revolution, Keith Devlin describes how basic ...