To
randomize a
deck of cards by splittling it in
half and then... well,
shuffling them back together.
A few years ago, a pair of mathematicians decided to calculate how many typical shuffles it would take to completely randomize a deck. They abstracted a poker deck into a fifty-two-dimensional space, then calculated the number of random shuffles it would take to make the dimensions equally distributed.1 Their answer: seven.
1 I have only their word for it that this was actually the simplest approach.