Any real number a between 0 and 1 has a decimal representation, written 0.d1 d2 d3…, where each di is one of the digits 0, 1, 2,…, 9; this means that
This notation can be extended to enable any positive real number to be written as
using, for the integer part, the normal representation cncn−1…c1c0 to base 10 (see base). If, from some stage on, the representation consists of the repetition of a string of one or more digits, it is called a recurring or repeating decimal. For example, the recurring decimal 0.12748748748…can be written as or as , where the dots above indicate the beginning and end of the repeating string. If the repeating string consists of a single zero, this is generally omitted and the representation is called a terminating decimal.
The decimal representation of any real number is unique except for terminating decimals which have two expansions, as with 0.25 and . The numbers that can be expressed as recurring (including terminating) decimals are precisely the rational numbers.