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Seven standard "riffle" shuffles are needed to effectively randomize a 52-card deck.
(lemmy.dbzer0.com)
this post was submitted on 01 Jan 2025
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Autism
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I've always found this factoid pretty dubious. First off it's statistical so there are no absolute truths or facts, only tendencies.
But do this experiment for yourself, I just did a few times: take all the kings and aces out. Order them (I used Spade, Club, Heart, Diamond, Aces first then kings) and put them on top of the deck. Now do 7 riffles and look through the deck.
What I found is that the 8 chosen cards are still weighted towards the top of the deck (a little less than half moved to the bottom half, but none to the bottom 1/3rd). The suits got shuffled a little but all the spades and most clubs were still in the top 1/3rd of the deck. Most of the aces and kings stayed together in close pairs or triplets, within 5 cards of each other.
So no, 7 riffles isn't realistically good enough for fair play at actual tables. You need to mix in some cuts and pool shuffles to break up the structure of the deck and properly distribute the cards.
I do think cuts are necessary, and I use them each time. If each riffle includes a cut I feel this factoid is undoubtedly true, period.
Therefore, I think the definition of riffle must include a cut.