By the latter part of the first millennium of the Current Era, the system we use today to write numbers and do arithmetic had been worked out — expressing any number using just the ten numerals ...

This field has advanced our understanding of prime numbers, additive functions, and sequence distributions by introducing constraints on the digits that appear in numerical expansions.

Leonardo of Pisa, also known as Fibonacci, is best remembered today for introducing a sequence of numbers: 0, 1, 1, 2, 3, 5 and so on, each number after 0 and 1 equaling the sum of the two before it.