Unary coding, or the unary numeral system and also sometimes called thermometer code, is an entropy encoding that represents a natural number, "n", with "n" ones followed by a zero (if "natural number" is understood as "non-negative integer") or with "n" − 1 ones followed by a zero (if "natural number" is understood as "strictly positive integer"). For example 5 is represented as 111110 or 11110. Some representations use "n" or "n" − 1 zeros followed by a one. The ones and zeros are interchangeable without loss of generality. Unary coding is both a prefix-free code and a self-synchronizing code.