The sequence a_{1}, a_{2}, …. a_{n} (where a_{i} ≠ 0 for each i) is said to be in harmonic progression if the sequence 1/a_{1}, 1/a_{2}, … 1/a_{n} is in A.P.

The nth term of the H.P is given by a_{n} = 1 / a + (n - 1)d where a = 1 / a_{1 }and d = 1/a_{2} - 1/a_{1}

If a and b are 2 non - zero numbers then the harmonic mean of a and b is a number H

such that the sequence a , H, b is a H.P. We have, H = 2ab / (a + b)

If a_{1}, a_{2}, … a_{n} are n non - zero numbers then the harmonic mean H is given by

1/H= 1/N(1/a_{1} + 1/a_{2} +… 1/a_{n})