Given a list of numbers, is it possible to find out (or in other words, is there a statistical measure to tells the) the closeness of the numbers (do note that i am not talking about correlation - this would be for 2 sequences - something like correlation between height and weight).

I am looking for something like a closeness coefficient for a given series of numbers, so given a series [0,10,20,30,40] - the 'closeness coefficient' gives me the spread of the numbers.

It would also be nice if the 'closeness coefficient' depicts the 'density' of the numbers - but if this is a different computable statistical measure, then it shouldnt be a problem.