Does anyone have any suggestions on how to determine the formula to
generate
following number?

1.333, 1.5, 1.667, 1.75, 2, 3
If I insert 1 in cell A1, then 1.333 will be returned in cell B1.
Does anyone have any idea on what formula will generate this rhythm for
the
list of numbers?

There is none. If your 4th number were 1.833, then there would be a
relationship covering the first 5 numbers, but nothing would handle the jump
from 2 to 3 as the end of your series. On the off chance there is a
mistyping in your sequence, let's look at the first 5 numbers in more
detail. Although you stop the numbers at 3 decimal places, the .333 and .667
are obviously shortenings of the fractions 1/3 and 2/3. Let look at these
numbers as mixed numbers (whole number plus fraction). They are...

1-1/3 1-1/2 1-2/3 1-3/4 2

Changing them to pure fractions, they become...

4/3 3/2 5/3 7/4 2/1

Lets reformat them so they each have a denominator of 12. The changed
fractions become...

16/12 18/12 20/12 21/12 24/12

Look at the progression of the numerators... 16, 18, 20, 21, 24. If that 4th
number were 22 instead of 21, then we would have a series that increases by
2. But, in order for that to happen, the 4th number would have to be 22/12
and not 21/12. The fraction 22/12 is, in decimal form, 1.833 rounded to 3
decimal places. But even with that, there is no way to account for the huge
jump from 2 to 3 from your original sequence. The number 3 is the same as
36/12 and its numerator, 36, is 12 greater than 2's numerator when converted
to a numerator of 12, not the 26 one would expect if the series were to
continue.

Hence, there is no formula relationship that can cover the progression of
numbers you showed originally.

Rick