Possible rational approximation: f(x) = 1/7 * (2 + 5/x)
This gives
f(1) = 1
f(2) = 0.6429
f(3) = 0.5238
f(4) = 0.4643
Of course, given the limited precision of our data, it can be any value in a range of possible formulas. Assuming that it's of the form a + b/x, where a + b = 1 (so that f(1) is fixed at 1), a can be anywhere in interval [0.278, 0.286] (and therefore b [0.714, 0.722]).
I chose a to be 2/7 (~0.2857) in the above formula because it was the first "simple" fraction I came up with that fit in that range.
For the curious:
This gives
f(1) = 1
f(2) = 0.6429
f(3) = 0.5238
f(4) = 0.4643
Of course, given the limited precision of our data, it can be any value in a range of possible formulas. Assuming that it's of the form a + b/x, where a + b = 1 (so that f(1) is fixed at 1), a can be anywhere in interval [0.278, 0.286] (and therefore b [0.714, 0.722]).
I chose a to be 2/7 (~0.2857) in the above formula because it was the first "simple" fraction I came up with that fit in that range.
For the curious:
All fractions within range with denominator <100