Rank (Sequence)

The position of a Rational Number in the Sequence 1, ${\textstyle{1\over 2}}$, 2, ${\textstyle{1\over 3}}$, 3, ${\textstyle{1\over 4}}$, ${\textstyle{2\over 3}}$, ${\textstyle{3\over 2}}$, 4, ${\textstyle{1\over 5}}$, ..., ordered in terms of increasing Numerator+Denominator.

See also Encoding, Farey Series