Quoting from the math subreddit:
“Proof — easy numeric comparison. There are 52! possible orderings of a deck, and I’m assuming all are equally likely after your shuffling. Let’s wildly overestimate and assume that every second since the universe was created, a million decks of cards were shuffled and someone looked through them. Thus fewer than 10^24 orderings have ever been seen.
But at an incredibly crude estimate, 52! is at least 10^42 * 10!; let’s underestimate that again wildly by 10^42. That means that chances of your ordering ever having come up previously are at most 1 in 10^18.
(Note, by the birthday paradox, the chances that there have been two identical orderings observed by two people in history are quite a bit higher — perhaps even feasibly likely; I haven’t calculated it. But we’re looking here at the probability that a given ordering matches one of the ones previously seen.)“