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In [[mathematics]] and in particular in [[combinatorics]], the '''Lehmer code''' is a particular way to [[encoding|encode]] each possible [[permutation]] of a sequence of ''n'' numbers. It is an instance of a scheme for [[Permutation#Numbering permutations|numbering permutations]] and is an example of an '''[[inversion (discrete mathematics)|inversion]] table'''.
The Lehmer code is named in reference to [[Derrick Henry Lehmer]], but the code had been known since 1888 at least.<ref name="lehmer"/><ref name="laisant"/>
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Allegedly, [[Johannes Kepler]] clearly exposed this [[secretary problem]] to a friend of his at a time when he was trying to make up his mind and choose one out eleven prospective brides as his second wife. His first marriage had been an unhappy one, having been arranged without himself being consulted, and he was thus very concerned that he could reach the right decision.<ref name="ferguson"/><ref>http://www.math.upenn.edu/~ted/210F10/References/Secretary.pdf</ref>
==Similar concepts==
Two similar vectors are in use. One of them is often called inversion vector, e.g. by [[Wolfram Alpha]].
See also {{Section link|Inversion_(discrete_mathematics)|Inversion related vectors}}.
{{Portal|Mathematics}}
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