For more than you ever wanted to know on the mathematics of a perfect shuffle, see this paper: http://statweb.stanford.edu/~cgates/PERSI/papers/83_05_shuffles.

For more than you ever wanted to know on the mathematics of a perfect shuffle, see this paper: http://statweb.stanford.edu/~cgates/PERSI/papers/83_05_shuffles.pdf http://statweb.stanford.edu/~cgates/PERSI/papers/83_05_shuff... I saw one of the authors, Persi Diaconis, give a talk on this paper, and then perform a perfect shuffle. I was floored.