 From a mathematical analysis of the Gilbert – Shannon – Reeds model of random shuffles , one can show that the number of times one needs to shuffle an n @-@ card deck of cards , using riffle shuffles , to get a distribution on permutations that is close to uniformly random , is approximately 3 / 2 log2 n . This calculation forms the basis for a recommendation that 52 @-@ card decks should be shuffled seven times . 
