Your guess
How often do you have to riffle 52 cards until they're practically random?
What riffling is
To riffle, you split the deck into two halves and let them fall into each other. A mathematical model of this, the Gilbert–Shannon–Reeds model, has been shown in experiments to match how real people shuffle. One of the leading figures in the field is Persi Diaconis – mathematician and magician.
An unimaginable number
8 · 10⁶⁷possible orders exist for 52 cards
There are 52! ways to order 52 cards: 52 times 51 times 50 and so on down to 1. The result is roughly an 8 followed by 67 zeros.
Too perfectly shuffled
If you manage to riffle perfectly eight times in a row – card by card, with the top card staying on top – you're back to the original order. Such a perfect shuffle is controlled and doesn't make the deck random.
