In A1 enter:
..5
In A2 enter:
=A1+1/(ROW()*(ROW()+1)) and copy down
In B2 enter:
=(A2-A1)/A1 and copy down

For the first 10 rows:

0.50000000
0.66666667 33.3333333333%
0.75000000 12.5000000000%
0.80000000 6.6666666667%
0.83333333 4.1666666667%
0.85714286 2.8571428571%
0.87500000 2.0833333333%
0.88888889 1.5873015873%
0.90000000 1.2500000000%
0.90909091 1.0101010101%

and for rows 999 thru 1002:

0.99900000 0.0001002004%
0.99900100 0.0001000001%
0.99900200 0.0000998004%
0.99900299 0.0000996013%

so for i1000 the relative change term-to-term will be under your limit.
--
Gary''s Student - gsnu200797