Calculating Entropy

[Saxman]

I have a column with the following numbers. They are horse racing odds.
How would I calculate the entropy for these numbers; a measure of how
closely spaced the odds are (how competitive the race is).

7
21
4
9
15
17
7
26
21
21
15
13
15
34

 

[Saxman]

What is the formula for doing this manually?

I really don't know, but somebody who does, came up with the following
results for two sets of figures.

The first produced 222 and the second 146. I guess the higher the
figure, the less likely the race will be run true to form?

Entropy appears to be one of those phenomena that nobody can truly describe?

Often used with molecular/cellular structure?

Think of a group of people sitting on a greensward on a summers day.
It's kind of random. What are the chances of them all being herded
together? Not likely, but not impossible. Hence horseracing, not
likely, but not impossible.


3.5
4.5
13
4
3.75


26
41
6
13
1.22
26