Persi Diaconis showed in $1992$ that in order to shuffle a deck of $52$ cards, you need at least $7$ riffle shuffles.
However, in the paper he published, he showed that we needed $\frac{3}{2}\log_2n$ where $n$ is the number of cards in the deck.
$\frac{3}{2}\log_2 52 \approx 8.55$ which is not $7$.
Which answer is right$?$ Should we shuffle $7$ times or $9$ times$?$ I am guessing that the $7$ times comes from a different randomness metric, but I haven't found any article explaining it.
Thank you! :)