How are UQ Holder member numbers attributed? In page 12 of chapter 11, Touta and Kuroumaru are officially accepted in UQ Holder. They are, respectively, attributed the numbers 7 and 11:



Do these numbers mean anything in particular and correspond to something in terms of hierarchy (of power or ranking)? If so, how powerful/ranked are Touta and Kuroumaru?
Or are they just randomly chosen?
Not sure if this is considered canon, as I stopped reading the manga and am not sure if further details were revealed, but... 

On episode 3 of the anime, when Touta and Kuromaru meet Jinbei Shishido, he tells 'em he's number 2, and Kuromaru says:



Again, not sure if this is canon. Also not sure if Kuromaru is just making an assumption, or if this is a given in the anime — there are some different things in the adaptation, and I don't remember this bit of conversation from the manga. But, if this is not an assumption, then the numbers are attributed according to how powerful the characters are.