Fact time

So I was thinking about the number 5 just now, and I realized I know very little about it. It's always just kinda been a number to me. Of course, I can't leave that be now (mostly because I'm bored) so I did some research, and here it is:

5 (five) is...

thought to be the only odd untouchable number,
in base ten, the 1-automorphic number,
one of only two prime denominators of vulgar fractions that can be written as decimals without infinite repetitions.

Also, the roman numeral for 5 is V, which comes from an outstretched hand (okay...),
5 is the lightest atomic mass for which no stable isotopes occur for any element, and
Five is also the number of days left in the countdown.

But just for kicks, here's a list of dude's who did something that five fits in to (solution, set, pairing, whatever)

Fermat
Mersenne
Wilson
Eisenstein
Fibonacci
Pell
Markov
Perrin
Ruth-Aaron
Znám
Sierpinski
Abel-Ruffini

... mathmaticians have some strange names...