I'm trying to come up with a typographically appealing way to express "special" numbers such as the complex unit
i = sqrt(-1) or Euler's number
e. It has to be such that it cannot be confused with regular numbers (such as the running index
i, for example), and would ideally work for serif as well as sans-serif fonts.
I was briefly thinking of typesetting these numbers in bold, but found that bold face is often used to indicate vector quantities.
[Edit: Johannes Küster suggests to use upright for constants (about 14 minutes into his talk).]
I've seen double-stroked small letters too, and must say this isn't without appeal. I have no idea how to consistently typeset those, though. The (outdated?) bbm package seems to provide at least some basic functionality.
What do you use to represent special numbers, why do use it, and how to you typeset your solution?