I don't know if there is something wrong with what you wrote or what I read;

When n= 1, it is 4/5 on the left and 1/8 on the right, right?

If this is right,

Then just write a prescription directly;

An = (1/2) (2n+1)-1and then make a prescription;

But you will find that this is wrong; Below the root sign is a negative number;