To celebrate my ninth follower here - presumably also my 20th over on The Door, hello!
How significant are numbers in your game world?
Is it bad luck to have thirteen at the table, or in the adventuring party? Is three the magic number, or is it five, or seven? Which number Shall Not Be Spoken?
And how do you apply this when you have an uncertain number of PCs?
Of course, you can make just about any number, or phrase, or physical characteristic, hugely significant in a game world. Omens and pattern recognition have presented us with plenty of examples.
"Five there must be, one for each finger of the hand!"
"2001 is actually the start of the new millennium!"
"Nobody likes a math geek, Scully. "
"Ahh, you have green eyes, you cannot enter by the front door!"
So if you have six players, they could be connected by a prophecy relating to the six senses, the days God worked on Earth, or the luck of a normal die.
And since most RPGs run off numbers and their random generation, you could even throw number symbolism into the game itself. In Nomine, the game of angels and demons secretly battling over the world, is built around the d666.