Basic Information
An Arc Number is a number that pops up over and over again in a given work, often in seemingly unrelated contexts. Sometimes the number really is significant; sometimes, it's just an in-joke or Stock Shout Out. It's the numeric equivalent of Arc Words.
Sources
Literature: Most gamers are probably familiar with 42, the ultimate answer from the Hitchhiker's Guide series by Douglas Adams.
TV Series: On the show Lost, a set of possibly cursed numbers, (4, 8, 15, 16, 23, and 42) seem to haunt the characters. Those numbers (and 108, the total if they're added together) recur frequently, being the numbers of hotel rooms, airplane seats, lotto numbers, etc.
The number 23 has it's own mythology built up around it, as well.
Further Arc Number examples can be found at the TV Tropes Wiki
Game and Story Use
- Using the same number again and again can be a way to hint at the importance of an event, or make the players feel like a mystery is afoot. See also Arc Words
- Subtly using different arc numbers for different things can leave hints for your players. "Hang on, this probably isn't The Conspiracy's doing, they always do things in fours and there were five attackers. It isn't the cult either, they do sevens. Are we dealing with someone new?"
- Using numerology to pick an arc number can include other hints. An arc number of 13 or 108 is probably not a good sign.
- Sequences of arc numbers can hint at a Coded Myth. If your arc words come out of The Bible, for instance, you might use book, chapter, and verse for arc numbers without ever once actually saying the words.