Harry Potter and the most powerfully magical number

7

I've made a list of some significant references to the number seven in the Harry Potter series. Quite interesting.
The series is just awesome and I'm thankful to the person who's made a complete convert of me.

There are seven years of schooling in Hogwarts.

There are seven kids in the Weasley family.

Harry paid seven gold galleons for his wand, which is seven inches long.

There are seven players on each side in Quidditch.

As per "Quidditch Through the Ages", there are seven hundred ways of committing a Quidditch foul.

On of the obstacles on the way to the Philosopher's stone is a table with seven differently shaped bottles standing on it in a line . "Seven bottles: three are poison; two are wine; one will get us safely through the black fire, and one will get us back through the purple."

There were seven challenges guarding the Stone, the seventh of which is faced in. The challenges were:
Fluffy (set by Hagrid); the Devil's Snare (set by Sprout) ; the winged keys (set by Flitwick) ; the chess game (set by McGonagall) ; the troll (set by Quirrell) ; the riddle of the potions (set by Snape) ; the Mirror of Erised (set by Dumbledore) .

Arthur Weasley wins seven hundred Galleons in the Daily Prophet draw.

There are seven secret passages connecting Hogwarts to Hogsmeade.

The Triwizard Tournament was first established some seven hundred years ago.

The trunk in which Barty Crouch Jr. puts Moody has 7 keyholes.

The Room of Requirement is on the seventh floor.

Tom Riddle says "Wouldn't it be better, make you stronger, to have your soul in more pieces, I mean, for instance, isn't seven the most powerfully magical number, wouldn't seven -?"


Please feel free to add any other references. One reference, ofcourse, would be Harry's birth month (July) but I'm not sure how significant that is.