Leonardo Fibonacci, sometimes called Leonardo of Pisa, was a thirteenth-century Italian mathematician. He was instrumental in bringing the Arabic numbering system to Europe to replace the use of Roman numerals. He is also remembered for a series of numbers that now bears his name. The Fibonacci sequence starts with 1, 1 and each subsequent number is the sum of the two previous numbers. The first ten numbers in the Fibonacci series are: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55.