Despite being the last digit to come into use in the numerical system, the zero plays a central role in mathematics. During the 2nd century CE, Ptolemy began using a small circle with a long bar above it to symbolize zero. Because it was used alone, not just as a placeholder, this Hellenistic zero was perhaps the first documented use of a number zero in the Old World. Four centuries later, an Indian mathematician wrote a book of rules governing the use of the zero. Is zero an odd or even number? Discuss
Source: The Free Dictionary