Another elemental one can be found in Ye Olde Romspec: Vriska becomes infatuated with two Breath players (John, Tavros) because the atomic number of Oxygen is 8. (Similarly, but non-numeric, Kanaya has a moth mom and is drawn to Light players Vriska and Rose). The alpha kids are all tied to Noble Gases (because of their inert/Null Session) but I can't think of any uses of the corresponding numbers off the top of my head.... maybe Jane is Helium (2) because the alpha kids are the second human group/session?

Couple more that can get lost on archival readers:
- 11/11/11 is called "2x3 Prong Day" because it could be interpreted both as "two prongs, three times" (11 11 11) or "three prongs, two times" (HIC's Trident). (This is also the same day Skyrim came out, feel old yet?)

- Vriska has 8 dice with 8 sides, leading to a total of 8^8 effects. As Doc Scratch jokes about at one point, if you substitute one of the eights for a common variable like Y, you'd get 8^y , which looks like Hella Jeff's face. Also the result for 8^8, ie the total number of possibilities for Vriska's dice to land on, is 16,777,216 , which has the lucky 777, a completed backwards 612, and most of another backwards 612. But this is just math, how could Hussie have planned that unless...
- Someone already mentioned the trolls have 6+6=12 names, but it works for the kids too: all their first names are 4 letters, their last names can be *either* 6 or 7, 6 + 7 = 13