There are only 5 billion essentially distinct Sudoku puzzles (solutions) (proof here using Group Theory and Burnside's Lemma).

Interesting article on rating the difficulty of Sudoku's and various solving methods (including a short backtracking program written in Ruby).

Really interesting problem in recreational mathematics - try to reverse a unit line segment via translations/rotations - but in doing so sweep out a minimal area.

PI/4 is the obvious minimum - but it turns out you can do so in an arbitrarily small area.

What's odd to me, is that any combinations of moves that are either a) rotations about the center and b) translations, CAN NOT achieve an area less than PI/4; so it's counter-intuitive that you can do better than that.

random number generator, if you happen to need precalculated random numbers.
Not sure if you can specify a distribution (e.g. Gauss, Poisson, etc) yet.
Nope, you can't. Uniformly distributed only.

Quoted: RANDOM.ORG offers true random numbers to anyone on the Internet. The randomness comes from atmospheric noise, which for many purposes is better than the pseudo-random number algorithms typically used in computer programs.