title: Where are "Special Numbers" mentioned in Concrete Maths used?
body: <p>I was glancing through the contents of Concrete Maths online. I had at least heard most of the functions and tricks mentioned but there is a whole section on Special Numbers. These numbers include Stirling Numbers, Eulerian Numbers, Harmonic Numbers so on.  Now I have never  encountered any of these weird numbers.  How do they aid in computational problems?  Where are they generally used?</p>