What is Harmonic Progression ? What is Harmonic Series?

What is Harmonic Progression? What is Harmonic Series? Is there any formula to find sum to ‘n’ terms in a harmonic progression?

In mathematics, a harmonic progression is a progression formed by taking the reciprocals of an arithmetic progression. In other words, it is a sequence of the form
image
where ?1/ d is not a natural number.
the harmonic series is the divergent infinite series:
image
Every term of the series after the first is the harmonic mean of the neighboring terms.

There isn’t a good closed form expression. As a special case, one has the Harmonic numbers
There isn’t even a good closed form expression for this particular sum, although there is a good approximation
where
is the Euler-Mascheroni constant. Similar approximations can be given for more general sums of harmonic progressions.