Insert 4H. Ms. between 1 and 16.

The first and the last terms are easy to derive. From that,
the series will be 1/a, 1/A1, 1/A2, 1/A3, 1/A4, 1/b

These terms form HP. So, a, A1 A2 A3 A4 b form an AP.
So, d= (b-a)/(n+1) … n=4
So,A1 A2 A3 A4 are easily accessible using the general term formula of AP. Hence all the HP are also obtained.