For example, when we write a number like 1905, the value of each digit depends on its place in the number string. Here there are5 units,9 lots of one hundred(which is 10×10), and one lot of one thousand(which is 10×10×10). The use of the zero symbol is important as a placeholder. In the case of 1905, no contribution comes from the 10’s place, but we cannot ignore that andjust write195 instead, as that represents an entirely different number.Indeed, each string of digits represents a different number and it is for that reason that huge numbers may be represented by short strings. For instance, we can assign a unique number to every human being on Earth using strings no longer than ten digits and in this way give a personal identifier to every individual belonging to this huge set.