Gödel number
One of the simplest Gödel numbering schemes is used every day: The correspondence between integers and their representations as strings of symbols. For example, the sequence 2 3 is understood, by a particular set of rules, to correspond to the number twenty-three. Similarly, strings of symbols from some alphabet of N symbols can be encoded by identifying each symbol with a number from 0 to N and reading the string as the base N+1 representation of an integer.