Not that it ever matters in practice, but as some trivia, this number changes depending on your deck size. It’s 8 for 52 cards, 58 for 60 cards, 12 for 45 cards, and 21 for 49 cards. (And 30 for 77 cards, hello syntax)
It follows this sequence: http://oeis.org/A002326
[quote=“OEIS”]In other words, least m>0 such that 2n+1 divides 2^m-1.
Number of riffle shuffles of 2n+2 cards required to return a deck to initial state. [/quote]
(Actually I didn’t know that in advance, I just made a quick program to generate the sequence and then asked OEIS if it recognized it. Pretty cool huh?)
In practice when I shuffle I intersperse two or three overhand shuffles with a lot of smash shuffles, because otherwise a card that starts at the very top or bottom could stay there or move only a small distance away.