1. I assume that you are looking for the greatest number N such that the sum is less than 60. Right?

2. I didn't find a way to do the necessary calculations in one step, but I had to use 2 steps:

3. Switch the calculator into SEQ-mode.

4. Enter at y=

nMin=1

u(n)=5/(u(n-1))+1

(You'll find the u at 2ND 7)

5. Go to TBLSET

TblStart = 1

Tbl = 1

6. Create the sequence and store it into the list L1:

seq(u(n),n,1,21,1) STO L1

7. Next step

sum(L1)

8. To change the limits of the summation you can recall the last commands by using 2ND ENTER