Are there any prior (in universe) indications of seven being the most magically powerful number before Slughorn's memory?

Question

I have been reading a bunch of older questions here, and some of them are questioning the importance of Slughorn's memory in HBP, and I feel for good reason. The only explanation the story gives that the memory is important, is because it confirmed for Dumbledore that Voldemort wanted to make seven horcruxes. But the older questions here make good points. By that time Dumbledore already knew Voldemort had more than 1 horcrux, he possibly suspected Voldemort already had at least one horcrux by the point in time seen in Slughorn's memory, Voldemort might have been lying to Slughorn about this intentions to have seven horcruxes, he might have made more than seven just to be safe, he might not have had enough time to make anywhere close to seven, and so on. There were a number of things that could have been wrong about their conclusions from Slughorn's memory. In the end it even turned out that Voldemort finally ended up with an eight part soul, because he had no idea about the one that latched onto Harry. As far as story development goes, there were any number of other ways the story could have introduced the readers to the concept of Voldemort wanting a seven part soul, rather than providing us with the complicated side plot of Slughorn's tampered memory. If nothing else, Dumbledore could have just "guessed" that Voldemort would want seven horcruxes, as it has been implied numerous times in the story that his guesses are correct.

Given all this, was there any indication in the story, up to that point, of there being any significance to the number seven, or if having seven of anything made it magically significant/powerful/anything? I am specifically looking for canon, in universe, book answers. If there are any later explanations in author interviews or later publications, and if there is anything explained in the movie canon (keep in mind I am considering movie canon separate from book canon), it would be interesting information and you can include them in the answer, but I am specifically asking whether in the story, before the scene of Voldemort asking Slughorn 's opinion on seven horcruses, if any magical properties of seven have been explained. talked about, or shown directly.

Answer 1

Having checked every instance of the word “seven” in the books prior to the scene in question, there does not seem to be any indication of any special properties associated with the number. While there are several things that are seven (e.g. seven years at Hogwarts, seven players on a Quidditch team), there is nothing that shows any special significance to that number.

Answer 2

Seeing as JKR wrote these books while struggling with ideas about her Christian upbringing, it makes sense that the numbers 7 and 12 are the most prominent. 12 uses of dragons blood, 12 Christmas trees, etc.

I’m pretty sure it’s written to be one of those common superstitions. Like the Greeks believed in the power of threes. The Chinese have connotations for 7s and 13s.

Like the answer above mentioned, 7 players on a Quidditch team is one example. However, 7 years at school is simply the standard British system.

There’s not a lot of precedent to the number 7 in the books because it’s already implied to be a strong superstitious number from the author’s perspective. 7 days of the week, etc. I read online that 7 for Christians symbolises completion. I guess that’s why, in a twisted way, Voldemort thought of 7 as being the perfect number.

Breaking the fourth wall, JKR wrote seven books.