Superparticular

Superparticular numbers are ratios of the form (n+1)/n, or 1+1/n, where n is a whole number greater than 0. In ancient Greece they were known as Epimoric (επιμοριοσ, epimorios) ratios, which is literally translated as "above a part."

These ratios have some peculiar properties:

• The difference tone of the dyad is also the virtual fundamental.
• The first 6 such ratios (3/2, 4/3, 5/4, 6/5, 7/6, 8/7) are notable harmonic entropy minima.
• The difference (i.e. quotient) between two successive epimoric ratios is always an epimoric ratio.
• The sum (i.e. product) of two successive epimoric ratios is either an epimoric ratio or an epimeric ratio.
• Every epimoric ratio can be split into the product of two epimoric ratios. One way is via the identity 1+1/n = (1+1/(2n))*(1+1/(2n+1)), but more than one such splitting method may exist.
• If a/b and c/d are Farey neighbors, that is if a/b < c/d and bc - ad = 1, then (c/d)/(a/b) = bc/ad is epimoric.

Curiously enough, the ancient Greeks did not consider 2/1 to be superparticular because it is a multiple of the fundamental (the same rule applies to all natural harmonics in the Greek system).

See: List of Superparticular Intervals and the Wikipedia page for Superparticular number.