Leonardo Pisano Fibonacci (c.1170-1250), an Italian mathematician known for his pioneering work in the development of the decimal system that eventually replaced the Roman numeral system. In 1202, he published Liber abaci, which introduced the Hindu-Arabic place-valued decimal system and the use of Arabic numerals in Europe. Fibonacci is perhaps best known for a simple series of numbers, later named the Fibonacci numbers in his honor. The series begins with 0 and 1. After that, use the simple rule: Add the last two numbers to get the next. This produces the series: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987,... Fibonacci numbers show up in a surprising number of natural phenomena, including the branching pattern of some trees, the spiral design of the nautilus shell, the petal design on some flowers, and the structure of some pinecones.