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in a row
Shuffle a deck of 52 playing cards and there are 52! — 52 factorial — possible orders it could be in. That is 8.07 × 1067, a 68-digit number, roughly the number of atoms in the Milky Way. The deck in your hands has almost certainly never existed before and never will again.
52! turns that fact into a game. Two decks are shuffled and turned over side by side, and you watch how far the coincidence runs. In Until you miss, one wrong card ends the round — two in a row is already rarer than being dealt four of a kind. In All 52 pairs, you turn the whole deck and count the matches; the expected number is exactly one, and you score at least one about 63% of the time. Both modes end at the same wall, and nobody is getting through it.
Playing is free, there is nothing to buy, and every shuffle is committed with a SHA-256 hash before you play so you can check afterwards that it was not changed to suit the result.
Full rules for both modes · Where 8 × 1067 comes from · Verify a shuffle yourself · Questions