A sequence
whose reciprocals form an arithmetic sequence is called a harmonic sequence.
Example:
1, ½, 1/3, ¼…
The reciprocal form an arithmetic sequence.
In the harmonic sequence 2/3, ½, 2/5, 1/3, 2/7…
We
can say that ½ is the harmonic means between 2/3 and 2/5; ½, 2/5 and 1/3 are the
harmonic between 2/3 and 2/7.
2/3+1/2+2/5+… is a harmonic series.