[Tutor] A small math puzzle [recreational Python]

[Danny Yoo]

On Sat, 5 Jan 2002, Tim Peters wrote:

> [talking about derangements of words with duplicate letters]
> 
> FYI, you can compute this without exhaustive generation, but it's not
> simple.  See, e.g., section 4-7 (Permutations with Forbidden
> Positions) in Liu's "Introduction to Combinatorial Mathematics".

Thanks for the recommendation!  I just ordered it from Amazon.  Do you
have any other introductory math books you'd recommend for those who are
interested in this sort of stuff?