In mathematics, a harmonic progression (or harmonic sequence) is a progression formed by taking the reciprocals of an arithmetic progression.
Equivalently, a sequence is a harmonic progression when each term is the harmonic mean of the neighboring terms.
As a third equivalent characterization, it is an infinite sequence of the form
where a is not zero and −a/d is not a natural number, or a finite sequence of the form
where a is not zero, k is a natural number and −a/d is not a natural number or is greater than k.